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 (EOTi) by similar to 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/cm(2) at a capacitor voltage of 0.8 V).

Automated summary

This study compared the performance of ruthenium (Ru) thin films deposited via ALD as bottom electrodes for DRAM capacitors. Using DFM-ALD improved the surface morphology of the Ru films and increased the proportion of RuO2 formation during subsequent TiO2 ALD, leading to higher crystallinity in TiO2 films. Depositing bottom electrodes using DFM-ALD reduced the EOT values while still meeting DRAM leakage current density specifications.