LAUSR

Accurate characterization of thin films and geometric features including the cavities during and after the fabrication process is crucial for proper CMUT operation, reliability, consistent array operation, and improved yield. Three different optical profilometry techniques: white light interferometry, laser confocal microscopy, and structural grid illumination microscopy have been reviewed in this paper with a focus on characterization of various thin films and geometric features during different CMUT fabrication stages and post processing. The relative merits of each technique have been investigated experimentally in the context of CMUT fabrication for better characterization and process development. The surface roughness and diaphragm deformation results have also been compared with AFM data. From the review, it appears that characterization needs of CMUTs are unique and a combination of complex diversified characterization tools is necessary to generate sufficient data for design verification and functional optimization.