Tungsten Via Stack for MTJ Interconnect Diffusion Control
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Solution Overview
Problem
Copper used in back end of line (BEOL) processes for magnetoresistive random-access memory (MRAM) is prone to high electromigration and diffusion into insulating layers, leading to performance degradation and damage of the magnetic tunnel junction (MTJ).
Innovation Solution
A tungsten via is used between the lower magnetic layer of the MTJ and the copper interconnect, with additional tantalum nitride layers and an adhesion layer to prevent copper diffusion, fluorine corrosion, and tungsten peeling, while providing a copper diffusion barrier and reducing stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is used in BEOL processes for MRAM, then low resistivity and good conductivity are achieved, but copper electromigration and diffusion into insulating layers cause performance degradation and damage to MTJ
Solution Approach 1:
A tungsten via is introduced as an intermediary component between the copper interconnect and the MTJ. The tungsten via acts as a physical barrier that prevents copper atoms from migrating into the insulating layers and damaging the MTJ, while still allowing electrical connection to be established. This mediator structure eliminates the harmful copper diffusion pathway without compromising the low-resistivity advantage of copper interconnects.
Solution Approach 2:
The interconnect structure is segmented into multiple functional layers: copper interconnect for low-resistivity signal transmission, tungsten via for diffusion barrier and adhesion, and additional protective layers. This segmentation separates the functions of electrical conduction and diffusion prevention into distinct structural components, allowing each material to optimize its specific function without compromising the other.
2Object-generated harmful factors
If tungsten via is used to prevent copper diffusion, then copper electromigration is reduced, but tungsten peeling may occur reducing adhesion
Solution Approach 1:
The via structure is constructed as a composite material system with multiple layers including tungsten via, tantalum nitride layers, and adhesion layers. Each layer is selected for its specific properties: tungsten for diffusion barrier, tantalum nitride for fluorine corrosion protection, and adhesion layers for bonding strength. This composite structure combines the advantages of different materials while mitigating their individual weaknesses, preventing both copper diffusion and tungsten peeling simultaneously.
Solution Approach 2:
Adhesion layers and tantalum nitride layers are introduced as intermediary structures between the tungsten via and surrounding materials. These intermediary layers provide gradient transitions in material properties, reducing stress concentration and preventing direct contact between incompatible materials that would cause peeling. The adhesion layers specifically mediate the bonding between tungsten and other structures, ensuring mechanical strength.
3Reliability
If additional tantalum nitride layers are added to prevent fluorine corrosion and copper diffusion, then MTJ protection is improved, but device complexity increases
Solution Approach 1:
The tantalum nitride layers perform multiple functions simultaneously: they act as diffusion barriers for copper, protection layers against fluorine corrosion during processing, and stress management layers. By designing a single material layer that accomplishes multiple protective functions, the patent avoids the need for separate layers for each function, thereby reducing overall structural complexity while maintaining comprehensive MTJ protection.
Solution Approach 2:
Multiple protective functions (copper diffusion barrier, fluorine corrosion protection, stress reduction) are merged into a single integrated via structure with carefully engineered layers. Rather than adding separate structures for each protection mechanism, the patent combines these functions into a unified multi-layer via system where each layer contributes to multiple protective objectives, simplifying the overall device architecture.
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 reduces copper electromigration, prevents fluorine diffusion, and enhances the adhesion of tungsten, resulting in lower resistivity and improved reliability of the MTJ by preventing copper migration and corrosion.
Implementation Method 1
A tungsten via is used between the lower magnetic layer of the MTJ and the copper interconnect, with additional tantalum nitride layers and an adhesion layer to prevent copper diffusion
Implementation Method 2
an adhesion layer to prevent copper diffusion, fluorine corrosion, and tungsten peeling
Implementation Method 3
to prevent copper diffusion, fluorine corrosion, and tungsten peeling
Data Source
AI summary
One or more semiconductor processing tools may deposit one or more tantalum nitride layers on an upper surface of a copper interconnect and within a via. The one or more semiconductor processing tools may deposit an adhesion layer on an upper surface of the one or more tantalum nitride layers and within the via. The one or more semiconductor processing tools may deposit tungsten on an upper surface of the adhesion layer and within the via for via interconnection of the magnetic tunnel junction to the copper interconnect.