Improved Properties of the Atomic Layer Deposited Ru Electrode for Dynamic Random-Access Memory Capacitor Using Discrete Feeding Method

Ruthenium (Ru) thin films deposited via atomic layer deposition (ALD) with a normal sequence and discrete feeding method (DFM) and their performance as a bottom electrode of dynamic random-access memory (DRAM) capacitors were compared. The DFM-ALD was performed by dividing the Ru feeding and purge steps of the conventional ALD process into four steps (shorter feeding time + purge time). The surface morphology of the Ru films was improved significantly with the DFM-ALD, and the preferred orientation of the Ru films was changed from relatively random to a <101>-oriented direction. Under the DFM-ALD condition, the higher susceptibility of oxygen atoms to the Ru electrode resulted in a higher proportion of the RuO₂ formation on the Ru film surface during the subsequent TiO₂ ALD process. This higher RuO₂ portion leads to higher crystallinity of the local-epitaxially grown TiO₂ films with a rutile phase. Such improvement also decreased the interfacial component of equivalent oxide thickness (EOT_i) by ∼0.1 nm compared with the cases on sputtered Ru film, which showed an even smoother surface morphology. Consequently, the minimum EOT values when the Ru bottom electrodes deposited via DFM-ALD were adopted were 0.76 and 0.48 nm for TiO₂ and Al-doped TiO₂ films, respectively, while still satisfying the DRAM leakage current density specification (<10^-7 A/cm² at a capacitor voltage of 0.8 V).