Long-term environmental stability of residual stress of SiNx, SiOx, and Ge thin films prepared at low temperatures

Optical measurements of thin-film-stress-induced substrate bending have been employed in a characterization of long-term environmental stability of stress of low-temperature (<125 degrees C) plasma enhanced vapor deposited (PECVD) SiNx, as well as thermally evaporated SiOx, and Ge thin films for applications in micro-electro-mechanical systems (MEMS) fabricated on temperature sensitive, non-standard substrates. It has been found that in comparison to their stress values measured at atmospheric conditions, PECVD SiNx layers prepared below similar to 100 degrees C as well as layers of thermally evaporated Ge exhibit significantly more tensile (less compressive) stress values when measured in vacuum, which are reversible upon re-exposure to an atmospheric, dry nitrogen, helium, argon, or oxygen ambient. Raising the deposition temperature above similar to 100 degrees C results in PECVD SiNx stress being stable in vacuum and dry nitrogen storage, which is complemented by stress stability in laboratory atmosphere for films deposited above similar to 125 degrees C. Stress of thermally evaporated SiOx layers is stable in vacuum and undergoes compressive stress development in either dry nitrogen or laboratory air. (C) 2009 Elsevier B.V. All rights reserved.