Influence of post-deposition moisture uptake in polycarbonate on thin film's residual stress short term evolution

• High tensile stress jump observed in sputtered thin films deposited on polycarbonate
• Moisture uptake in the polymeric substrate identified as the origin of tensile stress transition.
• Stress transition is reversible and is directly related to the change in ambient humidity.
• The magnitude of tensile stress transition depends on the barrier effect of the deposited film.

The residual stress in a thin film can have a major impact on the durability and reliability of the coated device. After deposition and upon exposure to a new environment, a coated material is subjected to various external factors that might affect its stress and thus its overall performance. To identify a protocol to measure stress in a proper and repeatable manner for films deposited on polymeric substrates, we performed ex-situ profilometry measurements on thin dielectric and metallic films (30 nm) deposited on polycarbonate substrates that were stored under different environments over a 1–2 days aging period.We observed a significant tensile transition in the film stress, characterized by an extremum and a return to an equilibrium value within the first 24 h upon atmospheric exposure. Our analyses further revealed that this phenomenon was reversible and dependent on both the relative humidity and the integrity of the thin film. The moisture uptake and subsequent water vapor diffusion within the substrate, which induces an inhomogeneous volume change in the PC and results in extrinsic bending stresses, appears to be the cause of the stress evolution. A precise control of the post-deposition environment is required to measure the residual stress of thin films deposited on polymeric substrates.

Figure optionsDownload high-quality image (62 K)Download as PowerPoint slide