Residual stress control during the growth and release process in gold suspended microstructures

Abstract

This paper presents the growth and release process effects on the deformation of suspended gold micro-structures. Cantilever type test structures, typically used for RF MEMS devices have been examined. The structures have a thickness of 2μm, produced by patterned gold electro deposition above a sacrificial photoresist layer, then removed by dry release in oxygen plasma ashing and wet release using critical point dryer (CPD). The growth process of gold electroplating is optimized for low residual stress using pulse power supply. Minimum stress 35-60 MPa is obtained at grain size 30-45nm and RMS roughness of the order of 5-8nm. The growth mechanism of structural layer and releasing methods are optimized to obtain planar MEMS structures. The main parameters considered are the initial stress during the growth of electroplated gold and the release process recipes developed for fabrication of metallic structural layer.