Structural Investigation of the Silver-Polyimide Interface by Cross-Sectional Ten and Ion-Beam Sputtering

Abstract

When metals are deposited on polymers at low rates and elevated temperatures extended and non-uniform interfaces may form, the structural investigation of which requires special techniques. In this paper the morphology of the silver-PMDA-ODA boundary formed during vapor deposition of the metal at 360°C has been investigated by means of cross-section TEM and a radiotracer technique in combination with ion-beam sputtering (IBS) for depth profiling. Ag was found to form clusters at the interface, but nearly spherical Ag particles up to diameters as large as 28 nm were also observed within the bulk of the polymer. The formation of Ag clusters is also reflected in the depth profiles, which, in addition, provide direct evidence for the diffusion of single Ag atoms deep into the polyimide. Diffusivities in the range of 10^-21 - 10^-18 m²/s were determined for 300°C < T < 400°C. The Arrhenius plot is curved in accordance with a free-volume mechanism of diffusion. Cross-sectional TEM and low-energy IBS-depth profiling turned out to be an ideal combination for the investigation of extended metal-polymer interfaces.