A parylene coating based room temperature wafer-level attachment method for MEMS integration with zero applied force

This paper reports a wafer-level attachment method using parylene as an interlayer material for integrating various shaped and fragile substrates into MEMS processes. In the proposed method, the substrates are placed on a handle wafer containing pillars and perforations, and coated with a standard parylene deposition process realized at room temperature, with no applied force. The substrate and the handle wafer are attached to each other via formation of a parylene interlayer. Only poor attachment is observed by utilizing a handle wafer containing pillars alone, as parylene cannot perfectly penetrate through the structures. The parylene penetration is significantly improved by introducing perforations to the handle wafer. It is experimentally shown that, with a perforated handle wafer containing pillar structures having 20μm height and 4.5mm spacing, parylene completely fills the gap between the structures, and can successfully be used to attach substrates to each other. The shear strength between the attached substrates has been measured as 0.49MPa, proving the feasibility of the method for integrating various materials into MEMS processes. As a demonstrator for the utilization of the attachment method in the microfabrication processes of sensors and actuators, a fragile 7cm×7cm×190μm PZT sheet has been attached to a handle wafer and processed successfully through a sample set of standard MEMS processes.