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

Area of Science:

• Materials Science
• Nanotechnology
• Electrical Engineering

Background:

• Ruthenium (Ru) thin films are crucial bottom electrodes in dynamic random-access memory (DRAM) capacitors.
• Optimizing the deposition process for Ru films is essential for improving capacitor performance and reliability.
• Conventional atomic layer deposition (ALD) methods may not fully optimize Ru film properties for advanced memory devices.

Purpose of the Study:

• To compare the performance of Ru films deposited via conventional ALD and a discrete feeding method (DFM-ALD) as bottom electrodes for DRAM capacitors.
• To investigate the impact of DFM-ALD on the surface morphology, orientation, and interfacial properties of Ru thin films.
• To evaluate the resulting dielectric properties and leakage current of DRAM capacitors utilizing DFM-ALD deposited Ru electrodes.

Main Methods:

• Ruthenium (Ru) thin films were deposited using both conventional ALD and a modified DFM-ALD process.
• DFM-ALD involved dividing Ru feeding and purge steps into shorter intervals.
• The performance of Ru films as bottom electrodes was assessed in DRAM capacitor structures with TiO2 and Al-doped TiO2 dielectric layers.

Main Results:

• DFM-ALD significantly improved the surface morphology and altered the preferred orientation of Ru films to a <101>-direction.
• Enhanced RuO2 formation occurred on the Ru surface during subsequent TiO2 ALD when using DFM-ALD.
• This led to improved crystallinity of rutile-phase TiO2 and a reduced interfacial equivalent oxide thickness (EOTi) by ~0.1 nm.
• Minimum EOT values of 0.76 nm (TiO2) and 0.48 nm (Al-doped TiO2) were achieved, meeting DRAM leakage current specifications.

Conclusions:

• The discrete feeding method for ALD offers a superior approach for depositing Ru bottom electrodes for DRAM capacitors.
• DFM-ALD enhances the interfacial properties and dielectric performance by promoting favorable RuO2 formation and improving TiO2 crystallinity.
• This method provides a pathway to achieving lower EOT values while maintaining acceptable leakage current densities in advanced memory devices.