Multilayer Dielectric Barrier for Copper Interconnect Adhesion and Etch Selectivity
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Solution Overview
Problem
In modern integrated circuits, the increased circuit density and reduced dimensions lead to signal propagation delays due to high line-to-line capacitance and reduced conductivity of interconnect lines, which are not adequately addressed by replacing aluminum with copper and traditional dielectric materials, requiring improved diffusion barrier layers and etch selectivity to prevent copper contamination and electromigration.
Innovation Solution
A dielectric barrier layer stack is formed with a nitrogen-containing silicon carbide layer for adhesion, a silicon nitride layer for diffusion blocking, and a nitrogen-enriched silicon carbide layer for etch selectivity, maintaining high adhesion and etch control while reducing oxygen and moisture diffusion, thereby enhancing copper integrity and electromigration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer dielectric barrier is used to prevent copper diffusion, then copper contamination is blocked, but adhesion to copper and etch selectivity cannot be simultaneously optimized
Solution Approach 1:
The single dielectric barrier layer is segmented into three distinct layers: a first dielectric layer (e.g., silicon nitride) providing copper diffusion barrier, a second dielectric layer (e.g., silicon carbide) providing adhesion to copper, and a third dielectric layer (e.g., silicon oxynitride) providing etch selectivity. Each layer is optimized for its specific function, resolving the contradiction between diffusion blocking and the simultaneous optimization of adhesion and etch selectivity.
Solution Approach 2:
The barrier structure uses composite material architecture combining three different dielectric materials, each with tailored properties. The composite structure leverages the strengths of individual materials (copper barrier, adhesion, etch selectivity) to achieve overall performance that no single material could provide alone.
2Reliability
If copper is used to replace aluminum for lower resistance, then conductivity improves, but copper contamination of dielectric layers increases
Solution Approach 1:
The barrier structure segments the protection function into specialized layers: the first dielectric layer specifically targets copper diffusion blocking, while other layers handle adhesion and etch selectivity. This segmentation allows the copper barrier function to be optimized without compromising other requirements.
Solution Approach 2:
The multi-layer dielectric structure acts as an intermediary barrier between copper and the surrounding environment, preventing copper atoms from migrating into dielectric layers while still allowing the copper interconnect to function electrically. The first dielectric layer serves as the primary intermediary blocking copper diffusion.
3Reliability
If dielectric layer thickness is increased to improve diffusion blocking, then copper confinement improves, but etch process control deteriorates
Solution Approach 1:
The total barrier thickness is segmented across three layers with different functions. The third dielectric layer is specifically designed with appropriate thickness to provide etch selectivity, while the first layer provides copper confinement. This segmentation allows each layer to be optimized for its specific thickness requirement without compromising the other functions.
Solution Approach 2:
Different regions of the barrier structure have different thicknesses and material compositions optimized for local requirements. The first layer near the copper interface is optimized for diffusion blocking, while the third layer at the etch interface is optimized for etch selectivity with appropriate thickness for process control.
4Reliability
If nitrogen content in silicon carbide is increased to improve adhesion, then electromigration resistance improves, but dielectric permittivity increases
Solution Approach 1:
The nitrogen content is segmented across different layers: the second dielectric layer (silicon carbide) contains optimized nitrogen content for adhesion and electromigration resistance, while the third dielectric layer (silicon oxynitride) has different composition optimized for low permittivity and etch selectivity. This segmentation allows nitrogen content to be optimized for adhesion without unnecessarily increasing overall permittivity.
Solution Approach 2:
Each dielectric layer has local composition optimized for its specific function. The silicon carbide layer has higher nitrogen content for adhesion and electromigration protection, while the silicon oxynitride layer has composition optimized for low-k properties and etch selectivity, achieving local optimization of conflicting properties.
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 solution provides superior barrier characteristics, maintaining high adhesion and etch selectivity, reducing electromigration, and enhancing the overall performance of copper-based metallization layers by effectively confining copper and suppressing diffusion, thus improving the integrity and reliability of semiconductor devices.
Implementation Method 1
a first dielectric layer formed on the metal-containing region and having a first thickness... providing an adhesion to the underlying metal region
Implementation Method 2
a second dielectric layer formed on the first dielectric layer and having a second thickness... providing an efficient confinement of the copper-based metal
Implementation Method 3
a third dielectric layer formed on the second dielectric layer and having a third thickness... having enhanced etch selectivity
Data Source
AI summary
By providing a barrier layer stack including a thin SiCN layer for enhanced adhesion, a silicon nitride layer for confining a copper-based metal region (thereby also effectively avoiding any diffusion of oxygen and moisture into the copper region), and a SiCN layer, the total relative permittivity may still be maintained at a low level, since the thickness of the first SiCN layer and of the silicon nitride layer may be moderately thin, while the relatively thick silicon carbide nitride layer provides the required high etch selectivity during a subsequent patterning process of the low-k dielectric layer.