Intrinsic stress in thin metallic multilayers
Barth, Jonas (2018)
2018
Materials Engineering
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2018-03-07
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201802201288
https://urn.fi/URN:NBN:fi:tty-201802201288
Tiivistelmä
The ePD™ process (embedded PVD for Design Parts) by Oerlikon Balzers com-bines a magnetron sputtering metallization process with a UV (Ultraviolet) lacquer painting, to replace electroplating as a metallization process for decorative interiors and exterior car parts. Since most sputtered films exhibit residual stress, understanding the origin of this stress is very important. High residual stresses in the ePD™ systems can have a detrimental effect on its appearance due to the emergence of cracks, as well as on the loss of adhesion to the substrate.
In this thesis the residual stress and film structure of chromium (Cr) and zirconi-um (Zr) are studied as a function of (1) sputtering time, (2) target current, (3) sputtering pressure, (4) substrate rotation and (5) interrupted deposition. Additionally, existing models are tested which allow to predict the residual stress and therefore to deposit a stress designed layer stack. Lastly, the connection of UV lacquer thickness and residual stress is investigated.
Glass substrates have been coated in a research batch coater and afterward ana-lyzed. The residual stress was determined by means of substrate curvature method as well as by X-ray diffraction (XRD). The latter was also used to evaluate the phase, tex-ture and crystalline size. The development of the film surface morphology and film structure was investigated with the scanning electron microscope (SEM). Finally, Young’s modulus and hardness of the PVD films were determined.
The experiments revealed a strong connection of residual stress, texture, phase, surface morphology and film structure with the thickness of both materials. Tensile stress was observed for Cr, which also showed a rotationally random oriented (110)-out of plane fiber texture for thinner films and a single crystal-like structure for thicker films. Zirconium, always exhibiting compressive stress, showed an amorphous structure for the thin films which changes to a more crystalline structure with an increasing film thickness or by increasing the sputtering pressure. Raising the target power lead to an increase in tensile stress for Cr and an increase in compressive stress for Zr. Increasing the sputtering pressure decreased the tensile stress in Cr and increased the compressive stress for Zr. The interruption of the deposition process caused a change in the observed stress for only the thick Zr films. The existing theoretical models were able to explain the observed results and allowed to predict the overall residual stress in a Cr-Zr-Cr layer stack.
The results suggest that it is possible to tailor and predict the residual stresses in PVD single films and layer stacks if the connection between process parameters and film structure evolution as well as the stress generating mechanism are known.
In this thesis the residual stress and film structure of chromium (Cr) and zirconi-um (Zr) are studied as a function of (1) sputtering time, (2) target current, (3) sputtering pressure, (4) substrate rotation and (5) interrupted deposition. Additionally, existing models are tested which allow to predict the residual stress and therefore to deposit a stress designed layer stack. Lastly, the connection of UV lacquer thickness and residual stress is investigated.
Glass substrates have been coated in a research batch coater and afterward ana-lyzed. The residual stress was determined by means of substrate curvature method as well as by X-ray diffraction (XRD). The latter was also used to evaluate the phase, tex-ture and crystalline size. The development of the film surface morphology and film structure was investigated with the scanning electron microscope (SEM). Finally, Young’s modulus and hardness of the PVD films were determined.
The experiments revealed a strong connection of residual stress, texture, phase, surface morphology and film structure with the thickness of both materials. Tensile stress was observed for Cr, which also showed a rotationally random oriented (110)-out of plane fiber texture for thinner films and a single crystal-like structure for thicker films. Zirconium, always exhibiting compressive stress, showed an amorphous structure for the thin films which changes to a more crystalline structure with an increasing film thickness or by increasing the sputtering pressure. Raising the target power lead to an increase in tensile stress for Cr and an increase in compressive stress for Zr. Increasing the sputtering pressure decreased the tensile stress in Cr and increased the compressive stress for Zr. The interruption of the deposition process caused a change in the observed stress for only the thick Zr films. The existing theoretical models were able to explain the observed results and allowed to predict the overall residual stress in a Cr-Zr-Cr layer stack.
The results suggest that it is possible to tailor and predict the residual stresses in PVD single films and layer stacks if the connection between process parameters and film structure evolution as well as the stress generating mechanism are known.