Indirect Synthesis of Carbon-Free Perovskite SrTiO3 Thin Films via SrF2 and TiO2 ALD for DRAM Capacitors

초록

To meet the increasing demands for high-performance DRAM, the integration of high-k dielectric materials into three-dimensional capacitor structures is essential. SrTiO3 (STO) has emerged as a promising capacitor material owing to its high dielectric constant. However, atomic layer deposition (ALD) of STO is hindered by challenges such as carbon contamination originating from metalorganic Sr precursors or the ambient environment, as well as difficulty in achieving high crystallinity of the perovskite structure. In this study, ALD processes of SrF2 using a novel Sr precursor, Sr(dmts)(hfac)(2), combined with TiO2 deposited from (CpMe5)Ti(OMe)(3), enabled the formation of SrF2-TiO2 mixed phase, which was subsequently converted directly into perovskite STO by O-2 annealing. Since carbon was excluded during SrF2-TiO2 formation, and fluorine ions diffused out during O-2 annealing via an anti-Frenkel defect effect, high-purity STO was achieved, resulting in a film with no detectable carbon contamination in the bulk region and significantly reduced fluorine content. Furthermore, the incorporation of an Al2O3 barrier layer effectively suppressed intermixing with the underlying TiN electrode, ensuring stable dielectric properties. Electrical characterization of the resulting Pt/STO/Al2O3/TiN capacitor confirmed a high bulk dielectric constant of STO (similar to 90) and low leakage current density (<10(-7) A/cm(2) at 0.8 V), demonstrating the feasibility of the indirect synthesis of thin-films for DRAM capacitors.

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