Correlation of Stress Relaxation and Microstructure Change in Polycrystalline Thin Films on Substrates: Au on Si <100
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CORRELATION OF STRESS RELAXATION AND MICROSTRUCTURE CHANGE IN POLYCRYSTALLINE THIN FILMS ON SUBSTRATES:
Au on Si at RT A.C. Vermeulen, R. Delhez and E.J. Mittemeijer Delft University of Technology, Laboratory of MaterialsScience, Rotterdamseweg 137,2628 AL Delft, The Netherlands.
ABSTRACT Stress relaxation in polycrystalline layers can be explained by processes, in which the microstructure plays a dominant role. The microstructure itself may also be subjected to changes. With X-ray diffraction information about both the stress and the microstructure can be obtained without destroying the specimen and without disturbing the stress relaxation process. In this paper a model system is studied: Au on Si. The specimens showed a simultaneous decrease of macrostress and dislocation density with time at room temperature. This could be interpreted on the basis of a model founded on thermally activated dislocation motion. It followed that the grain size is an important parameter for the change of the dislocation density.
INTRODUCTION Stress levels in polycrystalline layers tend to decrease [e.g. 1,4], even at room temperature [e.g. 2]. A description of relaxation as a function of time [1,2] results from the recognition that stress induced dislocation glide is hindered by obstacles, which are passed by thermal activation [5]. Hence the dislocation density will influence the relaxation. In this paper X-ray diffraction has been applied because it does not disturb the relaxation process. Moreover it allows to determine macrostress and dislocation density simultaneously and non-destructively. Au layers on Si have been investigated at room temperature. A strong correlation between stress relaxation and change of dislocation density has been found.
EXPERIMENTAL Gold layers of about I }jim thickness were made by physical vapour deposition (deposition rate -1 nm/s) in high vacuum (pressure
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