Graded Interconnect Cap for Copper Diffusion and Capacitance Control
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Solution Overview
Problem
Copper interconnects in semiconductor devices are susceptible to oxidation and diffusion into adjacent materials, and conventional sealing layers with high dielectric constants increase capacitance in the BEOL wiring stack.
Innovation Solution
A graded cap is formed by nitriding a metal cap on the interconnect, creating a microstructure that transitions from metal to metal nitride, which acts as a localized sealing layer to prevent copper diffusion and oxidation while reducing capacitance by using a material with a lower dielectric constant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional sealing layer with high dielectric constant is formed to prevent copper oxidation and diffusion, then copper protection is improved, but capacitance in the BEOL wiring stack increases
Solution Approach 1:
The patent applies parameter changes by transitioning the cap layer material composition from a uniform high dielectric constant material to a graded structure where the dielectric constant varies through the thickness. The cap layer contains a first portion with higher dielectric constant near the copper interconnect and a second portion with lower dielectric constant toward the upper surface, optimizing both protection and capacitance characteristics
Solution Approach 2:
The patent uses composite materials by creating a graded cap layer that combines multiple materials or compositional variations within a single continuous structure. This graded composition provides a transition from metal-like properties at the copper interface to dielectric properties at the upper surface, achieving both protective and low-capacitance functions
2Reliability
If a metal cap is formed to prevent copper oxidation, then copper protection is improved, but the cap material must be subsequently nitrided to prevent copper diffusion
Solution Approach 1:
The patent applies preliminary action by forming the metal cap layer with specific compositional characteristics before the nitridation process. The graded composition is established during deposition, preparing the structure to receive nitrogen diffusion in a controlled manner that creates the desired protective gradient without requiring additional complex processing steps
3Reliability
If a graded cap with graded microstructure is formed by nitriding, then copper diffusion prevention is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies parameter changes by utilizing the nitridation process to transform the metal cap's chemical composition and physical properties. The controlled nitrogen diffusion changes the material parameters through the cap thickness, creating a gradient in chemical composition, density, and dielectric constant that prevents copper diffusion while maintaining manufacturing feasibility
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 graded cap effectively prevents copper oxidation and diffusion, reducing the overall capacitance of the BEOL wiring stack and improving adhesion to dielectric layers without the need for a conventional sealing layer.
Implementation Method 1
forming a graded cap by nitriding the metal cap
Implementation Method 2
adversely impact the capacitance within the BEOL metalization or wiring stack
Data Source
AI summary
A graded cap is formed upon an interconnect, such as a back end of line wire. The graded cap includes a microstructure that uniformly changes from a metal nearest the interconnect to a metal nitride most distal from the interconnect. The graded cap is formed by nitriding a metal cap that is formed upon the interconnect. During nitriding an exposed one or more perimeter portions of the metal cap become a metal nitride with a larger amount or concentration of Nitrogen while one or more inner portions of the metal cap nearest the interconnect may be maintained as the metal or become the metal nitride with a fewer amount or concentration of Nitrogen. The resulting graded cap includes a gradually or uniformly changing microstructure between the one or more inner portions and the one or more perimeter portions.