Reducing membrane warpage to prevent overkill at MEMS visual inspection

Abstract

This study demonstrates the control of membrane warpage variation within micro-machined thermopile infrared sensor wafer to prevent overkill during automatic visual inspection process. The mechanism of warpage generation is discussed in view of total stress and buckling mode of the membrane. We controlled the total film stress of membrane by optimizing the stress of each thin film layer, especially SiO2 and SiNx layer, to suppress the higher-order buckling modes. As a result, only the first-order buckling mode appeared and the appearance of the membrane was made uniform within the wafer. This result indicates that the stress control considering buckling modes is effective when designing commercial MEMS products with laminated membrane structure.