Reversible Stress Relaxation during Precoalescence Interruptions of Volmer-Weber Thin Film Growth

From in situ stress measurements, we have observed that a large component of the precoalescence compressive stress that develops during Volmer-Weber growth of polycrystalline Cu films relaxes reversibly. This phenomenon is similar to the reversible stress relaxation previously observed in the postcoalescence regime. We have also observed that less than a tenth of a monolayer of deposition leads to an instantaneous stress of order 1 GPa. The stress changes in both the precoalescence and postcoalescence regimes of growth are explained by changes in the adatom population during and after deposition.

Figure 1

Plot of stress-thickness versus thickness for an experiment performed with a continuous deposition flux (dashed line) and another experiment with two growth interruptions followed by continuous deposition (solid line). Inset: Schematic representation of the typical evolution of stress-thickness vs thickness during Volmer-Weber growth of fcc metals; (a) prior to coalescence, (b) during coalescence, (c) during postcoalescence thickening, (d) a tensile rise during a growth interruption, and ( e) compressive stress development upon resumption of deposition.

Figure 2

Plot of the stress-thickness as a function of time for the experiment shown as the solid curve in Fig. 1.

Figure 3

The instantaneous stress versus thickness from the experiment shown in Figs. 1, 2. The first three large compressive spikes in instantaneous stress correspond to precoalescence growth cycles. The fourth spike corresponds to an interrupt performed well into the postcoalescence regime.