Bilayer-Cladded Cu Interconnects for Low-EM Scaling
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Solution Overview
Problem
The scaling of copper (Cu) interconnects to smaller device dimensions and feature sizes in integrated circuits poses challenges for gap fill and increased demands for electromigration (EM) performance, with existing solutions like adding dopants to the Cu seed layer resulting in residual dopant atoms that increase resistance and EM risk.
Innovation Solution
A thin adhesion layer is used as a liner to clad the bottom and sides of Cu interconnects, allowing for the formation of an ultrathin conformal Cu seed layer, which enhances bonding and reduces Cu diffusion, while capping the top surface with the same adhesion layer material minimizes EM risk and cap depletion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If dopants are added to the Cu seed layer to improve adhesion, then bonding strength is improved, but residual dopant atoms increase resistance and EM risk
Solution Approach 1:
The adhesion layer is segmented into two distinct layers: a first adhesion layer in contact with the barrier layer, and a second adhesion layer in contact with the Cu interconnect. This segmentation allows each layer to be optimized for its specific function - the first layer for adhesion to the barrier, and the second layer for adhesion to Cu while preventing dopant contamination
Solution Approach 2:
The bilayer adhesion structure acts as an intermediary system between the barrier layer and Cu interconnect. By introducing this intermediate structure, the patent avoids direct contact between Cu and dopant-containing layers, thus preventing dopant diffusion into Cu while maintaining adhesion through the two-layer configuration
2Productivity
If feature sizes are scaled down to increase device density, then productivity is improved, but gap fill and EM performance deteriorate
Solution Approach 1:
The patent applies different materials and properties to different locations within the interconnect structure. The bilayer adhesion configuration provides locally optimized adhesion at the Cu-barrier interface, enabling reliable gap fill in high-aspect-ratio trenches that would be difficult to fill uniformly with conventional single-layer approaches
3Productivity
If feature sizes are scaled down to increase device density, then productivity is improved, but adhesion and Cu diffusion control become more difficult
Solution Approach 1:
The adhesion function is segmented into two layers, where the first layer provides the primary adhesion interface with the barrier layer, and the second layer provides the Cu-facing adhesion interface. This segmentation creates a more stable configuration that better controls Cu diffusion at scaled dimensions
Solution Approach 2:
The bilayer adhesion structure functions as a composite material system combining two different adhesion layer materials. This composite structure provides enhanced stability and control over Cu diffusion compared to single-layer approaches, particularly important for maintaining composition stability at smaller feature sizes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach extends the use of Cu for feature sizes below 45 nm pitch, reduces interconnect resistance, and significantly improves EM reliability by preventing Cu diffusion and cap depletion, thus enhancing the performance and reliability of Cu interconnects.
Implementation Method 1
a barrier layer is conformally deposited onto the bottom and sidewalls of the trench. Then, a first layer of a bilayer adhesion layer or so-called liner is selectively deposited on the barrier layer
Implementation Method 2
An electroplating process is then used to fill the via and trench with copper metal to form the interconnect
Data Source
AI summary
Techniques are disclosed for providing cladded metal interconnects. Given an interconnect trench, a barrier layer is conformally deposited onto the bottom and sidewalls of the trench. A first layer of a bilayer adhesion liner is selectively deposited on the barrier layer, and a second layer of the bilayer adhesion liner is selectively deposited on the first layer. An interconnect metal is deposited into the trench above the bilayer adhesion liner. Any excess interconnect metal is recessed to get the top surface of the interconnect metal to a proper plane. Recessing the excess interconnect metal may include recessing previously deposited excess adhesion liner and barrier layer materials. The exposed top surface of the interconnect metal in the trench is then capped with the bilayer adhesion liner materials to provide a cladded metal interconnect core. In some embodiments, the adhesion liner is a single layer adhesion liner.