Formation of β-FeSi2 thin films on non-silicon substrates

Abstract

β-FeSi2 films were prepared on non-silicon substrates by sputtering. The crystalline growth, stress induced cracks and adhesive ability to the substrate were investigated on substrate temperature and thermal expansion coefficient of substrate materials. It was found that crack formation in β-FeSi2 films was dependent on the thermal expansion coefficients of CaF2, MgO and quartz glass insulating materials. High-density cracks were observed from β-FeSi2 films on CaF2 and quartz glass substrates with large difference of the thermal expansion coefficient between β-FeSi2 film and substrate materials, and it was crack-free on MgO substrate with a thermal expansion coefficient close to that of β-FeSi2 films. Polycrystalline β-FeSi2 films grew on Mo, Ta, W, Fe and stainless steel (SS) substrates at low substrate temperature around 400 °C. There was no α-FeSi2 phase confirmed in the films. All the films had continuous structures without noticeable cracks even though they have different thermal expansion coefficients. Capacity–voltage measurements showed that β-FeSi2 films formed on SS substrates has n-type conductivity, with residual carrier concentrations of about 1.3∼6.4×1018 cm−3. Auger electron spectroscopy depth profile measurements identified homogeneous distribution of Fe and Si atoms in the film region, but with a large interface region between the film and the substrate.