Piezo Metrology Concept
The monitoring and controlling of piezoelectric material is at least as important as the deposition itself. Different levels of quality checks can be done requiring different time frame after deposition, details can be defined together with customer. The basic material parameters like film thickness, refractive index and stress are obtained within hours after deposition on product or test wafers. But those parameters are not suitable to assess the piezo performance. The crystal quality is one factor impacting the piezoelectric performance. This can be measured by XRD within a day on test wafers.
The defect monitoring is crucial, especially for PZT, to maintain a good quality. Here regular measurements on product / test wafers is performed continuously since 2016 at Bosch.
The basic piezoelectric parameters like d33 and e31 or polarization contain better information regarding performance. For this again separate test wafers are prepared and measured on AixACCT tools.