Ruthenium Capping Layer for Liner-Free Cobalt Interconnect Stability
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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, which complicates their integration due to the absence of barrier layers.
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
1Device complexity
If liner-free conductive structures are used to reduce manufacturing complexity and improve conductivity, then contact resistance decreases and manufacturing steps are reduced, but cobalt out-diffusion occurs during thermal processing leading to material migration and reliability issues
Solution Approach 1:
The conductive structure is segmented into multiple functional layers: a liner-free cobalt base layer for low contact resistance, and a separate ruthenium capping layer for thermal stability. This segmentation allows each layer to perform its specialized function without compromising the other, resolving the contradiction between manufacturing simplicity and thermal reliability.
Solution Approach 2:
The ruthenium capping layer acts as an intermediary barrier between the cobalt conductive structure and the upper metallization layers. It mediates the thermal processing effects, preventing cobalt out-diffusion while allowing the liner-free structure to maintain its low contact resistance advantage.
2Reliability
If barrier layers are added to prevent cobalt out-diffusion, then thermal stability improves, but contact resistance increases and manufacturing complexity increases
Solution Approach 1:
The barrier function is applied locally only where needed - at the top surface of the conductive structure where thermal diffusion occurs - rather than applying a complete barrier layer throughout. The ruthenium capping layer provides localized protection against cobalt out-diffusion while leaving the sidewalls and bottom open, maintaining low contact resistance at the critical interface.
Solution Approach 2:
The conductive structure uses a composite material system combining cobalt (for low contact resistance) and ruthenium (for thermal stability and diffusion barrier properties). This composite approach allows the structure to simultaneously achieve low contact resistance and high thermal stability without requiring thick barrier layers that would increase contact resistance.
3Reliability
If ruthenium capping layers are implemented to prevent cobalt migration, then contact resistance is maintained and thermal stability improves, but additional manufacturing steps are required
Solution Approach 1:
The ruthenium capping layer is applied in advance, before upper metallization layers are deposited. This preliminary action prevents cobalt migration proactively during subsequent thermal processing steps, avoiding the need for corrective measures later in the manufacturing process and reducing overall manufacturing complexity.
Solution Approach 2:
The ruthenium capping layer performs multiple functions simultaneously: it serves as a diffusion barrier to prevent cobalt out-diffusion, provides thermal stability during processing, and maintains low contact resistance at the interface. This multi-functionality reduces the need for separate layers for each function, minimizing the increase in manufacturing steps.
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 liner-free conductive structures.
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.