Using Atomic Layer Etching for Precise Fabrication of 2nm Semiconductor Nodes

The Evolution of Semiconductor Scaling and the Need for Atomic Precision

Semiconductor manufacturing has long followed Moore's Law, which predicted the doubling of transistors on a chip every two years. However, as process nodes shrink to 2nm and below, traditional etching techniques such as reactive ion etching (RIE) face significant challenges in maintaining precision, uniformity, and material selectivity. Atomic layer etching (ALE) has emerged as a critical enabler for next-generation fabrication, offering atomic-scale control that is essential for 2nm node production.

Understanding Atomic Layer Etching (ALE)

Atomic layer etching is a cyclic, self-limiting process that removes material layer-by-layer, often just one atomic layer at a time. Unlike conventional plasma etching, which relies on continuous reactive species bombardment, ALE separates the process into discrete steps:

• Surface Modification: A precursor gas modifies the top atomic layer of the substrate.
• Removal: A secondary reactant or energy source selectively removes the modified layer.

This two-step approach ensures precise material removal while minimizing damage to underlying layers, making it ideal for complex 3D structures in advanced nodes.

Technical Advantages of ALE in 2nm Fabrication

1. Sub-Nanometer Precision

ALE achieves etch rates as low as 0.1–1 Å/cycle, allowing for unprecedented control over feature dimensions. At the 2nm node, where gate lengths approach 12–15nm and fin widths are just a few atoms thick, such precision is non-negotiable.

2. Superior Selectivity and Uniformity

ALE's self-limiting nature ensures high selectivity (>100:1 for materials like Si/SiO₂) and uniformity across 300mm wafers with less than 1% variation. This reduces defects and improves yield in high-aspect-ratio contact (HARC) and gate-all-around (GAA) FETs.

3. Damage-Free Etching

Traditional RIE introduces ion bombardment damage, degrading carrier mobility in ultra-thin channels. ALE's gentle removal mechanism preserves critical interfaces, such as high-κ/metal gate stacks in 2nm transistors.

Key Applications in 2nm Node Manufacturing

Gate Patterning for GAA Transistors

Gate-all-around (GAA) nanosheet FETs require exacting etch control to define stacked Si/SiGe channels. ALE enables:

• Precise SiGe sacrificial layer removal without Si channel undercut.
• Atomic-scale trimming of Si fins to achieve sub-5nm thicknesses.

Self-Aligned Via and Contact Formation

At 2nm, via pitches shrink below 30nm. ALE allows:

• Damage-free dielectric etch stops on ultra-thin copper barrier layers.
• Anisotropic etching of low-κ dielectrics with aspect ratios >20:1.

3D NAND and DRAM Scaling

ALE is critical for >200-layer NAND flash, enabling:

• Uniform channel hole etching through alternating ON/O stacks.
• Selective removal of sacrificial nitride in staircase contacts.

Challenges and Material Considerations

While ALE offers transformative capabilities, key challenges persist:

• Process Speed: Cyclic ALE is slower than continuous RIE, requiring optimization for high-throughput manufacturing.
• Material Systems: Developing chemistries for novel materials (e.g., ruthenium interconnects, ferroelectric HfO₂) remains an active research area.
• Plasma Integration: Advanced pulsed/radical-enhanced ALE systems must balance precision with equipment complexity.

The Future: ALE in Sub-2nm and Beyond

As the industry looks toward sub-2nm nodes (1.8nm, 1.5nm), ALE will play an even more pivotal role in:

• CFET (Complementary FET) Fabrication: Enabling vertical stacking of nMOS/pMOS with atomic-level interface control.
• 2D Material Integration: Precise patterning of transition metal dichalcogenides (TMDs) like MoS₂ for post-silicon channels.
• Quantum Devices: Atomically-defined qubit structures in silicon spin-based quantum computers.

Conclusion

Atomic layer etching represents a paradigm shift in semiconductor manufacturing, providing the atomic-scale fidelity required for 2nm node production and beyond. As the industry pushes against fundamental physical limits, ALE's ability to combine precision, selectivity, and material versatility will make it indispensable in the coming decade of advanced chip fabrication.