Stress Compensation Effect in AlN/Mo/AlN/Polysilicon Stack for MEMS Application

This paper presents the stress compensation effect in AlN/Mo/AlN stack and polysilicon layer. The stress of AlN/Mo/AlN and polysilicon layers was measured separately and together using Film Stress Measurement (FSM) tool. It was observed that stress of the combined stack of AlN/Mo/AlN shows opposite nature than the polysilicon. On combining the stack of AlN/Mo/AlN Mo on poly silicon results in a stress compensating effect. Cantilever beam of AlN/Mo/AlN stack and polysilicon was release separately. It was observed that cantilever beam of AlN/Mo/AlN stack show positive stress gradient and poly (poly-Si) cantilever beam show negative stress gradient. The cantilever beam of AlN/Mo/AlN stack on polysilicon after releasing shows almost flat beam. It means that positive stress gradient of 1µm AlN/0.2 µm Mo/25nm AlN seed stack compensate the negative stress gradient of 4.5 µm polysilicon.