Mechanical and Optical Properties of The Films of Tantalum Oxide Deposited by Ion-Assisted Deposition
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MECHANICAL AND OPTICAL PROPERTIES OF THIN FILMS OF TANTALUM OXIDE DEPOSITED BY ION-ASSISTED DEPOSITION P.J. MARTIN, A. BENDAVID, M.V. SWAIN, R.P. NETTERFIELD, T.J. KINDER, W.G. SAINTY AND D.DRAGE CSIRO Division of Applied Physics, Sydney Australia 2070 ABSTRACT Thin films of tantalum oxide 1 pm thick were deposited by oxygen ion-assisted electronbeam evaporation onto silicon and glass substrates. The packing density and optical properties of the films were controlled by the degree of ion assistance during growth. The films were characterized for hardness by ultra-micro indentation measurement and density by RBS. A strong correlation of hardness, and optical properties was found with the ion-to-vapor arrival ratio at the substrate during deposition. Evaporated films without ion assistance were found to be relatively soft with hardness values of 5.3 GPa and 6.5 GPa on glass and silicon respectively when measured with a Berkovich indenter. When the ion bombardment was increased the film hardness increased to a maximum hardness of 10 GPa for 1000 eV 02 ion bombardment. The measured microhardness of the films was found to be influenced by the nature of the substrate for all depositions with higher microhardness values being recorded for films deposited onto silicon. The films were found to be amorphous and homogeneous. Additional ultramicrohardness measurements with a spherical tipped indenter enabled the depth dependence of hardness and modulus to be determined. INTRODUCTION The microstructure of thin films plays a dominant role in determining the physical properties such as density and hardness and these properties in turn influence others such as the optical refractive index 1 . The degree of porosity in deposited thin films may be controlled by bombarding the growing film with energetic particles. The refractive index of most dielectric films is both increased and stabilised through bombardment induced densification mechanisms. The most common method of achieving film densification is ion-assisted deposition (LAD) in which material is evaporated by electron beam bombardment and the depositing film is irradiated with low energy ions, usually 02+ in the case of oxide deposition. Although there have been many studies of the influence of LAD on the optical properties of dielectric films there have been few investigations of the correlation in optical and mechanical properties. Here we report on the preparation of thin films of Ta2 O5 and the effects of IAD on the optical refractive index, film density and microhardness. EXPERIMENTAL METHOD The experimental arrangement for film deposition is shown in Fig. 1. The films were deposited in a cryo-pumped vacuum chamber by electron beam evaporation of high purity material (Superior Evaporants Inc, 99.9% pure). The base vacuum of the system was lx10-4 Pa. The deposition rate was fixed at 0.5 nm s- 1. The system was also equipped with two ion sources. The first source was a Commonwealth gridless ion gun operated at an anode potential of 160 V (equivalent to a mean energy of appr
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