Oxidation of hydrogen doped tantalum films on silicon

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Abstract
Hydrogen doping of Ta films before thermal oxidation affects the dc leakage current in oxidized Ta films. Metal-insulator-semiconductor (MIS) capacitors of Al/Ta2O5 (40 nm thick)/Si-substrate structures have been prepared for the electrical measurements. The Ta films were reactively sputtered on p-type Si substrates in a mixture of Ar and H2 gases suitable for hydrogen doping. The hydrogen doping was found to be effective in reducing the leakage current in the Ta2O5 films to be less than 10−3 times that of undoped films, especially after low temperature oxidation at 400 °C. Secondary ion mass spectrometry (SIMS) analysis showed that the incorporation in the Ta2O5 films of Si from the substrate was decreased by the presence of hydrogen during sputtering. A possible explanation for the reduction of leakage current caused by hydrogen doping is that the prevention of Si entry into Ta2O5 films reduces the density of oxygen vacancies induced by unsaturated SiOx(x<2). This is thought to suppress the Poole–Frenkel-type conduction in the Ta2O5 films.

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