MTJ Diffusion Barrier Layer for Copper Out-Diffusion Control
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Solution Overview
Problem
Metal out-diffusion from interconnect layers into magnetic tunnel junction structures disrupts the operation of magnetic random access memories (MRAMs), leading to reading errors and charge leakage.
Innovation Solution
Formation of a cobalt (Co) or ruthenium (Ru) diffusion barrier layer over copper interconnects connected to the magnetic tunnel junction structures, or using a copper-free tungsten (W) metallization to prevent metal out-diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If copper interconnects are used in interconnect layers, then electrical conductivity is improved, but metal out-diffusion into MTJ structures occurs causing reading errors and charge leakage
Solution Approach 1:
A diffusion barrier layer comprising cobalt (Co) or ruthenium (Ru) is introduced as an intermediary between the copper interconnect and the MTJ structure. This barrier layer prevents direct contact and diffusion of copper atoms into the MTJ, eliminating the harmful effect while allowing the copper interconnect to maintain its electrical conductivity function.
Solution Approach 2:
The interconnect structure is segmented into distinct functional layers: the copper interconnect layer for electrical conduction, the diffusion barrier layer (Co or Ru) for preventing atom migration, and the MTJ structure for memory function. This segmentation isolates the copper from the MTJ while maintaining electrical connectivity through the barrier layer.
2Reliability
If a diffusion barrier layer is added between copper interconnects and MTJ structures, then metal out-diffusion is prevented improving reliability, but device complexity increases
Solution Approach 1:
The diffusion barrier layer is applied selectively only in regions where copper interconnects contact MTJ structures, rather than uniformly across the entire device. This localized application prevents diffusion only where needed, maintaining reliability without unnecessarily increasing complexity in other regions of the device.
3Reliability
If copper-free tungsten metallization is used, then metal out-diffusion is prevented improving reliability, but electrical conductivity deteriorates
Solution Approach 1:
The solution merges the advantages of two materials: copper's high electrical conductivity and tungsten's diffusion resistance. The copper interconnect maintains electrical conductivity while the Co/Ru diffusion barrier layer provides the diffusion protection that tungsten would offer, achieving both reliability and conductivity without using copper-free metallization.
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
Prevents metal out-diffusion, maintaining the integrity and functionality of MRAMs by blocking the migration of copper atoms to the junctions, thereby reducing reading errors and ensuring stable operation.
Implementation Method 1
Formation of a cobalt (Co) or ruthenium (Ru) diffusion barrier layer over copper interconnects connected to the magnetic tunnel junction structures
Implementation Method 2
using a copper-free tungsten (W) metallization to prevent metal out-diffusion
Data Source
AI summary
The present disclosure describes an exemplary method that can prevent or reduce out-diffusion of Cu from interconnect layers to magnetic tunnel junction (MTJ) structures. The method includes forming an interconnect layer over a substrate that includes an interlayer dielectric stack with openings therein; disposing a metal in the openings to form corresponding conductive structures; and selectively depositing a diffusion barrier layer on the metal. In the method, selectively depositing the diffusion barrier layer includes pre-treating the surface of the metal; disposing a precursor to selectively form a partially-decomposed precursor layer on the metal; and exposing the partially-decomposed precursor layer to a plasma to form the diffusion barrier layer. The method further includes forming an MTJ structure on the interconnect layer over the diffusion barrier layer, where the bottom electrode of the MTJ structure is aligned to the diffusion barrier layer.