Vertical and Lateral Copper Transport through Graphene Layers

Area of Science:

• Materials Science
• Solid State Physics
• Nanotechnology

Background:

• Copper (Cu) diffusion is a critical issue in microelectronics, necessitating reliable diffusion barriers.
• Graphene is explored as a potential alternative to traditional barrier materials like tantalum nitride (TaN).

Purpose of the Study:

• To investigate the mechanism of Cu transport through single-layer graphene (SLG) diffusion barriers.
• To quantitatively assess the effectiveness of graphene as a Cu diffusion barrier and compare it with TaN.
• To explore the impact of graphene quality (grain size) and stacking on barrier performance.

Main Methods:

• Time-dependent dielectric breakdown (TDDB) tests were employed to evaluate Cu diffusion.
• A modified E-model was used to project low-field barrier effectiveness from high-field accelerated stress data.
• The performance of single-layer graphene and multi-transferred graphene stacks was compared to 4 nm TaN.
• The influence of graphene grain size on Cu vertical transport was analyzed.

Main Results:

• Single-layer graphene (3.5 Å) demonstrated a mean time-to-fail comparable to 4 nm TaN.
• Multi-transferred graphene stacks showed 2x and 3x improvements in barrier performance over SLG at 0.5 MV/cm.
• Large-grain (10-15 μm) SLG exhibited a 2-orders-of-magnitude longer lifetime than small-grain (2-3 μm) SLG.
• Cu transport mechanisms were found to differ at various stress electric field regimes.

Conclusions:

• Graphene is a viable and effective diffusion barrier for copper, with performance competitive against industry standards.
• Improving graphene quality, specifically increasing grain size or using single-crystalline graphene, is more beneficial for barrier reliability than increasing thickness via multi-transfer.
• The findings suggest potential applications for graphene as diffusion barriers for other metals in electronic devices.