A study of heating rate and texture influences on annealing hillocks by a statistical characterization of Al thin-film topography

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Abstract
In order to study the quantitative influence of thin-film elaboration conditions on annealing hillock characteristics, an original statistical analysis of profilometer recording was performed. It allows, with suitable hypothesis on hillock shape, a determination of the true hillock volume per unit area. On various annealed Al-Si-Ti films this volume decreases when the degree of preferred orientation increases. On both Al and Al-Si-Ti films an increase of heating rate induces a decrease of hillock volume. We developed a stress relaxation model where relative relaxing mechanism contributions are computed versus grain size and heating rate. Our experimental results interpreted through this model confirm the preponderance of grain boundary diffusion mechanisms in mass transport during hillock growth. The correlation between preferred orientation and hillock volume in Al-Si-Ti films is found to be related to both grain boundary diffusivity and grain size. The absence of small hillocks on high-temperature-deposited Al-Si-Ti films is discussed.