Doped Barrier Alloy for Low Resistivity BEOL Interconnects
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Solution Overview
Problem
The electrical resistance of vias in back-end-of-line (BEOL) interconnects in integrated circuits becomes a significant source of resistance at ultra-scaled dimensions, particularly at high via densities, necessitating a reduction in electrical resistance.
Innovation Solution
An interconnect barrier layer is formed using an alloy of an interconnect barrier material and a dopant element, where the dopant element is doped interstitially or substitutionally to increase the density of states, resulting in improved conductivity and reduced resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional barrier materials are used in ultra-scaled interconnects, then barrier function is maintained, but electrical resistance increases significantly
Solution Approach 1:
The patent applies parameter changes by doping the barrier material with specific elements (e.g., carbon in TaN, oxygen in TiN) to modify its electrical properties. This changes the resistivity parameter of the barrier material from typical values (e.g., 200-500 μΩ·cm) to lower values (e.g., 50-150 μΩ·cm), reducing the harmful electrical resistance effect while maintaining the barrier function against metal diffusion.
Solution Approach 2:
The patent uses composite materials by creating doped barrier layers where a base barrier material (TaN, TiN, CoW) is combined with dopant elements (C, O, B, Si). This composite structure maintains the essential barrier properties while introducing improved electrical conductivity through the dopant-induced changes in the material's electronic structure and defect density.
2Reliability
If barrier material density is increased to improve barrier function, then barrier effectiveness improves, but conductivity decreases
Solution Approach 1:
The patent changes the material parameters by introducing dopants that modify the electronic band structure and carrier concentration. For example, carbon doping in TaN increases the density of states at the Fermi level, which improves electrical conductivity without significantly compromising the physical barrier density and effectiveness against metal diffusion.
Solution Approach 2:
The patent applies local quality by creating regions with different dopant concentrations within the barrier layer. The dopant distribution can be optimized locally to achieve the right balance between barrier effectiveness and conductivity in different regions of the interconnect structure, particularly at interfaces where electrical contact is critical.
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
The increased density of states in the alloy leads to a decrease in resistivity, specifically reducing the vertical resistivity of the conductive metal/barrier interface and the overall interconnect stack, thereby addressing the high resistance issues in BEOL interconnects.
Implementation Method 1
The barrier layer includes an alloy, the alloy including an interconnect barrier material and a dopant element. A density of states of the alloy may be at least 50% greater than a density of states of the interconnect barrier material. In the alloy, the dopant element may be doped in the interconnect barrier material interstitially and/or substitutionally.
Data Source
AI summary
A method of forming an interconnect for an integrated circuit includes: identifying an interconnect barrier material, identifying a plurality of potential dopant elements, creating an ensemble of potential barrier structures including the interconnect barrier material doped at a plurality of doping positions and a plurality of doping amounts for each of the plurality of potential dopant elements, calculating a density of states for each of the barrier structures of the ensemble, selecting a dopant element and a doping amount based on the density of states, and depositing a barrier layer including an alloy, the alloy including the interconnect barrier material and the selected dopant element at the selected doping amount.