Super-selective cryogenic etching for sub-10 nm features.

Area of Science:

• Materials Science
• Nanotechnology
• Plasma Physics

Background:

• Plasma etching is crucial for transferring lithographic masks to materials.
• Shrinking feature sizes present challenges, particularly with thin masks, often requiring costly hard masks.
• Existing methods face limitations in achieving high selectivity and resolution at the nanoscale.

Purpose of the Study:

• To develop a high selectivity soft mask pattern transfer method using cryogenic plasma etching.
• To enable low-cost, high-throughput sub-10 nm nanofabrication.
• To investigate cryogenic SF(6)/O(2) gas chemistry for silicon etching.

Main Methods:

• Utilized inductively coupled plasma (ICP) etching with SF(6)/O(2) gas chemistry under cryogenic conditions.
• Focused on optimizing selectivity by minimizing photoresist etch rates.
• Investigated etching behavior for feature sizes ranging from large (400 nm-1.5 μm) to deep nanoscale (10 nm).

Main Results:

• Achieved high selectivity (around 140:1) with a photoresist mask for 1.5 μm features, demonstrating anisotropic profiles.
• Maximized selectivity on larger features by minimizing photoresist etch rates.
• Observed reduced selectivity at the deep nanoscale but still achieved high selectivity for 10 nm scale, high aspect ratio etching with thin polymeric masks.
• Noted gentler ion bombardment leading to planar-dependent etching and faceted sub-100 nm features.

Conclusions:

• Cryogenic SF(6)/O(2) plasma etching offers a viable pathway for high selectivity soft mask pattern transfer in sub-10 nm nanofabrication.
• The process is low-cost, high-throughput, and low-damage compared to traditional hard mask methods.
• The technique shows promise for advanced nanoscale fabrication despite selectivity challenges at the deepest scales.