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.
A comparison of dry and wet release methods for surface micromachining of metallic structures, such as RF MEMS switches, test structures, bridges, and cantilevers is presented. The dry release process is optimized by varying the concentration of O 2 and CF 4 plasma and RF power. The plasma ashing of the sacrificial layer typically results in damage to metallic structures or stress-related deformation due to rise in temperature (>80°C ). A wet release process using critical point drying (CPD) has been investigated to realize gold-electroplated structures with reduced residual stress. The CPD, being a low-temperature (31.1°C) process, is more suitable for compliant structures without any deformation.
Wafer-level micro-encapsulation is an innovative, low-cost, wafer-level packaging method for encapsulating RF MEMS switches. This article presents an approach for design and processing steps related to encapsulation of individual RF components e.g. CPW, RF MEMS switches, in view of the variation in performance subsequent to packaging. Bottom contact vertical packaging is more prone to misalignment margin and easy to make connections. Cavity height of 30 µm is optimized for bottom contact vertical packaging.