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SYME: Mechanical Properties of Thin Films

SYME I: HV I

SYME I.1: Hauptvortrag

Dienstag, 12. März 2002, 14:30–15:00, H 16

Stress and Structure Evolution During Formation of Polycrystalline Films — •Carl V. Thompson, Cody A. Friesen, and Steven C. Seel — Dept. of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA

High-sensitivity measurements of the bending forces exerted on substrates during nucleation, pre-coalescence growth, coalescence and post-coalescence growth of polycrystalline films have been made. In addition, measurements of stress evolution as a function of deposition rate and during interruptions of growth have been made at all stages of growth.

Cu deposited on fused-silica substrates is in a compressive state prior to coalescence, and evolves into a tensile state during coalescence. These films evolve back into a compressive state during post-coalescence thickening but interruptions of growth during post-coalescence thickening lead to reversible tensile relaxations of some or all of the compressive stress. We argue that the reversible stress evolution that occurs during interruptions of growth is associated with evolution of the shapes of grain surfaces. This argument is quantitatively supported by simulations, based on the level-set technique, of morphological evolution during growth and during growth interruptions, and by analyses of the effects of shape evolution on the forces exerted by the deposit on the substrate. These models are consistent with a wide range of data, both in prediction of the magnitudes of the stress changes, and in predictions of the kinetics of stress evolution.