Thermally Driven Self-Limiting Atomic Layer Etching of Metallic Tungsten Using WF₆ and O₂

Area of Science:

• Materials Science
• Chemical Engineering
• Semiconductor Manufacturing

Background:

• The semiconductor industry requires advanced etching techniques for sub-10 nm transistor fabrication.
• Self-limiting atomic layer etching (ALE) is crucial for manufacturing complex transistor structures.

Purpose of the Study:

• To demonstrate a thermally driven ALE process for tungsten (W) using sequential exposures of O2 and WF6.
• To understand the reaction mechanisms and determine optimal conditions for W etching.

Main Methods:

• Experimental investigation using quartz crystal microbalance (QCM) for the O2/WF6 etch process.
• Thermodynamic modeling to analyze temperature dependence and reaction pathways.
• Ex situ analysis using spectroscopic ellipsometry (SE), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS).

Main Results:

• A self-limiting ALE process for W was achieved at 300 °C with an etch rate of ~6.3 Å/cycle.
• Etching occurs readily at 300 °C but not below 275 °C, attributed to WO2F2 volatility.
• O2 provided more controllable etching than O3, with minimal fluorine incorporation observed post-etching.

Conclusions:

• The demonstrated W ALE process is effective for precise metal removal in semiconductor fabrication.
• Understanding the reaction mechanism enhances the knowledge base for ALE processes.
• This work expands the available ALE processes for advanced material processing.