Solid state dewetting of thin polycrystalline molybdenum films on sapphire

We investigated the agglomeration of the thin polycrystalline Mo films deposited on sapphire. The morphology evolution of one and the same sites region of the film was tracked with the aid of atomic force microscopy after consecutive interrupted annealing heat treatments at a constant temperature (0.4 Tm , where Tm is the melting point of Mo) by AFM imaging.

The formed dewetting holes exhibited both the elevated material rim containing abnormal grains and the rimless sections. Despite of the presence of these rimless sections, applying the JMAK model to the obtained data on holes growth supported the classical Brandon-Bradshaw`s model of dewetting based on curvature-driven surface diffusion [1]. This apparent contradiction was resolved by suggesting that the holes growth is controlled by the lateral flow of the material along the rimless sections toward preferred abnormal grains. The proposed model bears some similarities to the dewetting model of Jiran and Thompson [2], yet it predicts a rich variety of hole morphologies consistent with our experimental observations.

[1] R.H. Brandon, F.J. Bradshaw, Technical report, Royal Aircraft Establishment, Farnborough, 1966.

[2] E. Jiran, C.V. Thompson, J. Electron. Mater. 19 (1990) 1153