Mechanical effects of galvanic corrosion of thin film polysilicon
Mechanical, and electrical effects generated by the galvanic corrosion of polysilicon immersed in various hydrofluoric acid (HF)-based solutions are described. Micromachined test structures consisting of phosphorus-doped polysilicon in contact with a gold metallization layer are utilized. A suite of otherwise identical test (metal added) and reference (no metal) structures were used to investigate changes in key performance parameters. Corroded test structures demonstrate an increase in through-thickness strain gradient, a decrease in the characteristic frequency of mechanical resonance, no change in in-plane strain, greatly increased electrical resistance, a decrease in hardness, and a decrease in elastic modulus. Noteworthy results were observed for aqueous- hydrochloric acid, ethanol, water, ammonium fluoride (found in buffered oxide etchant), Triton-X-100, as well as vapor-HF based chemistries. This first systematic study validates preliminary experiments and demonstrates the impact of corrosion on miniaturized structures, indicating a potential influence upon the material properties, design, performance, fatigue, tribology (friction/ wear), manufacture, and packaging of micro- and nano-scale devices. Copyright © 2005 by ASME.
