Dynamic Hardness of Thin Films and its Thickness Dependence
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When the force and displacement is continuously measured while indentation is made, the hardness and other mechanical properties will be derived from the relation between indentation load and indentation depth, then that is called dynamic hardness. With nano-indentation technique, which uses very low load with accurate control, the dynamic hardness is an effective way to analyze the hardness and other properties of thin film materials [4,5]. In this paper, we measured the dynamic hardness of three kind of thin films, namely indium tin oxide, silica and chromium, deposited on the glass substrates [6]. Their dependence on deposited film thickness and also indentation depth will be discussed. The dynamic hardness of some engineering ceramics and fused silica were also measured. EXPERIMENT Thin films of lidium tin oxide (ITO), silica (SiO) and chromium (Cr) were deposited on the soda-lime-silica glass substrates, which were prepared by float method and were grounded and polished to Rmax of 5.5nm. Their chemical compositions and some of their physical properties are shown in Table 1. ITO films were deposited by DC magnetron sputtering method with the indium oxide target containing 10wt% of tin oxide. SiO 2 films were grown by electron beam 199
Mat. Res. Soc. Symp. Proc. Vol. 505 © 1998 Materials Research Society
evaporation method with pure silica source. Cr films were deposited by RF magnetron sputtering method with metal target of purity over 99.9%. Several kinds of deposited film thickness were used in this work, as is shown in Table 2. Table 1. Chemical compositions and some physical properties of the soda-limesilica glass substrate. Compositions Si0 2
A1203 Fe 20 3 CaO+MgO
Na20+K20 Table 2.
wt%
I
73 0.6
I
Transition Temp. Thermal Expansion
825 K 9x 10 6 /K3
I
Poisson's Ratio
0.23
0.1 13.0
13.3
Characteristics
Bulk Density Young's Modulus
2.5 g/cm 73 GPa
Thickness of the thin films used in this work. Film ITO SiO 2 Cr
Thickness 48, 50, 50,
99, 100, 100,
197, 193, 200,
(nm) 476, 494, 300
970 1018,
2036
The surface structures of glass substrate and thin films were observed by the atomic force microscope (AFM, Seiko Instruments Inc., SP13700 ), which are shown in Fig.1, and their surface roughness parameters, Ra and Rz, are in Table 3. The surface of glass substrate is very smooth with Ra of only 0.4nm. The Si0 2 film is similar to the glass substrate with a little larger Ra of 0.5nm. ITO film has very rough surface with Ra of 3.1nm and the structure is rather intricate. The surface of Cr film has elongated granular structure of about 100rnm in grain size. Table 3.
Surface roughness parameters of glass substrate and thin films
obtained from the atomic force microscope observations. Film Glass Substrate ITO (476nm) Si0 2 (2036nm) Cr (300nm)
Ra (nm) 0.4 3.1 0.5 1.8
Rz(nm) 2.7 20 4.0 15
Some commercially available engineering ceramics, namely silicon nitride (Si3N4 ), silicon carbide (SiC), alumina (A1 20 3) and toughened zirconia (ZrO2), and also fused silica (Si0 2) were used in this work
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