We use two kinds of specimen, the soft film / hard substrate system (amorphous silicon film deposited on (100) silicon) and the hard film / soft substrate system (amorphous germanium film deposited on PET (polyethylene terephthalate), to analyze the mechanical properties, stress distribution of the films and substrates.
The hardness and Young’s modulus of bulk PET (polyethylene terephthalate) obtained from nanoindenter are 0.3∼0.55GPa and 3.3GPa, respectively. The hardness and Young’s modulus of film/substrate system are fitted by equations provided by Nix [1]. A fitting equation that predict the Young’s modulus when the parameter β and the D/t ratio are given in the a-Ge film/ PET substrate where D is the penetration depth and t is the film thickness. The parameter β to the Young’s modulus is 1.62364. A fitting equation that predict the hardness when the H and indentation depth are given in the a-Ge film/ PET substrate. The parameter H0 and h* to the hardness are 3.95475GPa and 4.074867GPa where H0 is the hardness at infinite depth of indentation and h* is a characteristic depth.
The analytical method using curvature to measure stress and strain in films and substrates is studied. In a-Si film/ silicon substrate specimen, we find the tensile stress and compressive stress in the substrate increases with the increasing film thickness. The stress changes from compressive into tensile and the tensile stress increases linearly with z-axis near interface. We also find that stress in each film decreases with increasing film thickness and the stress will gradually decrease with z-axis thickness. In a-Ge film/ PET substrate, the tensile stress in the substrate increases with the increasing film thickness and if z-axis gradually closes to interface of substrate and film, the tensile stress decreases linearly. We also find that the film stress increases with the increasing film thickness as near the film/substrate interface. But the film stress decreases gradually with increasing z-axis close to substrate free surface.

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