Process Control Monitoring Devices for CMOS-MEMS Monolithic PMUT Technology

MEMS fabrication makes use of the know-how and fabrication methods inherited from semiconductors. Similarly multiple successive processing steps are required such as deposition, photo lithography, etching, CMP, etc. Each of these steps can introduce yield loss and hence advanced process control monitoring methods must be introduced to ensure its manufacturability.The paper describes an indirect measurement method approach for the sacrificial release process of PMUT devices on CMOS to overcome the limitations imposed by the traditional semiconductor foundry capabilities such as inline metrology and post fabrication destructive tests. By introducing dedicated sacrificial release design configurations and by measuring the dielectric properties of the release material it can be unequivocally proven the success of the release process at an early stage of the manufacturing process. Early detection of potential issues gives room for corrective action and reworks to improve the yield and keep competitive costs.