Rutile Without Substrate Limitations: Top-Interface-Driven Crystallization of TiO₂.

Area of Science:

• Materials Science
• Nanotechnology
• Semiconductor Device Physics

Background:

• Atomic layer deposition (ALD) control of polymorphic phases is crucial for high-k dielectrics in dynamic random-access memory (DRAM) capacitors.
• Rutile TiO₂ offers superior dielectric properties but faces integration challenges due to lattice mismatch with TiN electrodes.
• Current methods lack compatibility with DRAM processing temperatures and substrate requirements.

Purpose of the Study:

• To develop a substrate-agnostic method for stabilizing rutile TiO₂ within the thermal budget of ALD for DRAM applications.
• To overcome the lattice-matching limitations hindering rutile TiO₂ integration on TiN electrodes.
• To enhance the dielectric performance of DRAM capacitors using rutile TiO₂.

Main Methods:

• A top-interface stabilization strategy using a RuO₂ upper layer was employed to stabilize rutile TiO₂ at 400°C.
• Thickness-dependent phase mapping was used to study the anatase-to-rutile transition driven by interfacial energy.
• Methanol-assisted reduction-etching was utilized for selective RuO₂ removal post-deposition.

Main Results:

• The RuO₂ top layer successfully stabilized rutile TiO₂ irrespective of the underlying ZrO₂/TiN stack crystallinity.
• An interfacial-energy-driven transition enabled rutile formation even on amorphous ZrO₂.
• The resulting TiO₂/ZrO₂/TiN capacitors achieved a dielectric constant of ~80 and reduced equivalent oxide thickness.
• Selective RuO₂ removal was achieved with minimal TiN oxidation.

Conclusions:

• Top-interface engineering provides a versatile approach for stabilizing polymorphic oxides like rutile TiO₂.
• This method is compatible with DRAM process windows and can be extended to other advanced dielectric materials.
• The developed strategy overcomes substrate limitations, paving the way for improved DRAM capacitor performance.