Development of capacitive Micromachined Ultrasonic Transducer (II) - Analysis of Microfabrication Process

The main goal of this study was to develop a micro-fabrication process for the capacitive micromachined ultrasonic transducer (cMUT). In order to achieve this goal, the former research results of the micro-electro-mechanical system (MEMS) process for the cMUT were analyzed. The membrane deposition, sacrificial layer deposition and etching were found to be a main process of fabricating the cMUT. The optimal conditions for those microfabrication were determined by the experiment. The thickness, uniformity, and residual stress of the Si3N3 deposition which forms the membrane of the cMUT were characterized after growing the Si3N3 on Si-wafer under various process conditions. As a sacrificial layer, the growth rate of the SiO2 deposition was analyzed under several process conditions. The optimal etching conditions of the sacrificial layer were analyzed. The microfabrication process developed in this study will be used to fabricate the cMUT