Stress Characterization of Silicon Oxide, Silicon Nitride, Chromium and Gold Films for Micromechanics

In this work, the internal stress of grown silicon oxide, CVD silicon nitride, evaporated chromium and gold, conventionally used in micromechanics were investigated. Gold films were deposited both by PVD and electroplating, the latter using two different bath solutions (sulfite and cyanide). Stress measurements were carried out by wafer curvature comparison, before and after deposition, using Stoney`s formula for thin films: wafer curvature was measured by profilometer, The possibility to tailor the internal stess of electroplated gold was investigated, obtaining a stress range from tensile to compressive: Cyanide bath yielded stress from -30 MPa to about 0 MPa, and sulfite bath showed stress between -90MPa and 110 MPa. The obtained strss values can provede fundamental information for the design of micromechanic devices: particularly interesting is the stress of electroplated gold since this layer, combined with photoresist as a spacer, provides an excellent surface micromachining structural material for low temperature processing, with the possibility to set the internal stress of the micro structures by changing the plating parameter