Ruthenium Capping Layer for Cobalt Diffusion Control
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Solution Overview
Problem
Liner-free conductive structures in integrated circuits face challenges with cobalt out-diffusion during thermal processing, leading to increased contact resistance and material migration issues, which complicates the integration of ruthenium-filled conductive structures.
Innovation Solution
The implementation of ruthenium capping layers with specific properties, such as low electrical resistivity, high melting point, and low solubility in ruthenium and cobalt, is used to prevent cobalt out-diffusion and electromigration, formed between the ruthenium metal fill and upper metallization layers, functioning as a barrier to maintain low contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liner-free conductive structures are used to reduce contact resistance, then electrical conductivity is improved, but cobalt out-diffusion occurs during thermal processing leading to material migration issues
Solution Approach 1:
A ruthenium capping layer is introduced as an intermediary barrier between the cobalt-containing conductive structure and the upper metallization layers. This capping layer prevents cobalt atoms from diffusing outward during thermal processing while maintaining the liner-free structure's low contact resistance advantage. The ruthenium layer acts as a diffusion barrier without adding significant resistance to the electrical path.
Solution Approach 2:
The conductive structure is formed as a composite system combining cobalt (for low resistance), ruthenium (for diffusion barrier properties in the capping layer), and optionally other materials like tungsten or copper in the upper metallization layers. This composite approach allows each material to contribute its advantageous properties while mitigating their individual weaknesses.
2Ease of manufacture
If thermal processing is applied to integrate ruthenium-filled conductive structures, then material integration is improved, but cobalt migration increases leading to contact resistance degradation
Solution Approach 1:
The ruthenium capping layer serves as a protective intermediary that enables thermal processing to proceed effectively for integrating ruthenium-filled structures while preventing the harmful side effect of cobalt migration. This allows the manufacturing process to achieve good material integration without degrading the electrical contact resistance.
Solution Approach 2:
The ruthenium capping layer is formed on the conductive structure before the thermal processing steps are applied. This preliminary protective action ensures that when subsequent thermal processing occurs to integrate the ruthenium fill and other materials, the cobalt is already protected from migrating outward, thus maintaining contact resistance.
3Stability of the object's composition
If cobalt diffusion barrier layers are added to prevent out-diffusion, then material stability is improved, but device complexity increases
Solution Approach 1:
The solution uses a composite material approach where ruthenium serves dual purposes: as the fill material for the conductive structure and as the capping layer material providing diffusion barrier functionality. This eliminates the need for separate barrier layer materials and reduces structural complexity compared to using traditional multi-layer barrier systems.
Solution Approach 2:
The ruthenium material performs multiple functions: it provides the conductive fill in the structure and simultaneously serves as the diffusion barrier capping layer. This multi-functionality reduces the number of distinct material layers needed, thereby simplifying the overall device structure while maintaining material stability.
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 ruthenium capping layers effectively prevent cobalt migration into upper metallization layers, maintaining low contact resistance and thermal stability, thereby enhancing the integration and performance of ruthenium-filled conductive structures in integrated circuits.
Implementation Method 1
The ruthenium capping layers effectively prevent cobalt migration into upper metallization layers
Implementation Method 2
functioning as a barrier to maintain low contact resistance
Data Source
AI summary
The present disclosure describes a method for forming capping layers configured to prevent the migration of out-diffused cobalt atoms into upper metallization layers In some embodiments, the method includes depositing a cobalt diffusion barrier layer on a liner-free conductive structure that includes ruthenium, where depositing the cobalt diffusion barrier layer includes forming the cobalt diffusion barrier layer self-aligned to the liner-free conductive structure. The method also includes depositing, on the cobalt diffusion barrier layer, a stack with an etch stop layer and dielectric layer, and forming an opening in the stack to expose the cobalt diffusion barrier layer. Finally, the method includes forming a conductive structure on the cobalt diffusion barrier layer.