Atomic Layer Deposition of SrTiO₃ Films with Cyclopentadienyl-Based Precursors for Metal–Insulator–Metal Capacitors

The characteristics of the atomic layer deposition (ALD) of SrTiO3 (STO) films were examined for metal–insulator–metal capacitors, with Cp-based precursors Sr(iPr3Cp)2 and Cp*Ti(OMe)3 [Cp* = C5(CH3)5] employed as the Sr and Ti precursors, respectively. While the Sr precursor has a higher reactivity toward oxygen on the Ru substrate compared with another Ti precursor, with a 2,2,6,6-tetramethyl-3,5-heptanedionato ligand, which results in the highly Sr excessive STO film, the enhanced reactivity of the present Ti precursor suppressed the unwanted excessive incorporation of Sr into the film. A possible mechanism for the Sr overgrowth and retardation is suggested in detail. By controlling the subcycle ratio of SrO and TiO2 layers, stoichiometric STO could be obtained, even without employing a deleterious reaction barrier layer. This improved the attainable minimum equivalent oxide thickness of the Pt/STO/RuO2 capacitor to 0.43 nm, with acceptable leakage current density (∼8 × 10–8 A/cm2). This indicates an improvement of ∼25% in the capacitance density compared with previous work.