Atomic layer deposition of ruthenium at 100 °C using the RuO4-precursor and H2

Abstract

In this paper we report a low temperature (100 °C) ALD process for Ru using the RuO₄-precursor (ToRuS™) and H₂ as the reactant. The thermal decomposition behaviour of the precursor in the range of 50 °C–250 °C was investigated and it was found that thermal decomposition of RuO₄ to RuO₂ starts at a sample temperature of 125 °C. The RuO₄/H₂ process (0.0045 mbar/4 mbar) was attempted at temperatures below this decomposition limit and it was found that ALD growth of pure Ru is possible in a narrow temperature window near 100 °C. The growth rate during steady state growth was found to be 0.1 nm per cycle. The Ru film nucleated easily on a wide range of substrates (H-terminated Si, TiN, Pt and Al₂O₃). Although the films are grown at a low temperature, they are considerably pure and are of good quality as evidenced by a resistivity of 18 μΩ cm for an 18 nm film and a relative atomic concentration of impurities <5% as determined by XPS. It is hypothesized that the reaction of the RuO₄ molecule with the Ru-surface leading to a monolayer of RuO₂ is the mechanism that ensures a self-saturated behaviour of the first half reaction, which is a critical requirement to achieve a well-behaved ALD process.