MRAM Bottom Electrode Structure for CMP Planarization
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Solution Overview
Problem
Planarity variations between the bottom electrode and dielectric in magnetic tunnel junction (MTJ) devices lead to topography issues, causing poor grain growth and defects during the fabrication of MRAM devices due to dielectric dishing during chemical mechanical planarization (CMP) processes.
Innovation Solution
A bottom electrode structure with a recessed metal conductor, a conductive liner, and a cap material is used, where the conductive liner is harder than the cap layer, ensuring a surface roughness of less than 3 nanometers after planarization, minimizing dielectric dishing and achieving a flat, coplanar surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chemical mechanical planarization (CMP) is used to planarize the bottom electrode surface, then surface flatness is improved, but dielectric dishing occurs causing topography variations
Solution Approach 1:
A conductive liner is deposited on the recessed metal conductor surface before filling with cap material. This preliminary action creates a harder surface that resists CMP-induced dishing, preventing topography variations while maintaining surface flatness
Solution Approach 2:
The bottom electrode structure uses a composite construction with a recessed metal conductor, a conductive liner layer, and a cap material layer. This composite structure combines materials with different hardness properties to achieve both surface flatness and resistance to CMP dishing
2Ease of manufacture
If the cap layer is softer than the dielectric, then the cap layer is easier to deposit, but dielectric dishing occurs during CMP
Solution Approach 1:
The conductive liner material is selected to have greater hardness than both the cap layer and dielectric material. This parameter change in hardness prevents the cap layer from being pulled away during CMP, maintaining planarization accuracy while preserving deposition ease
3Productivity
If planarity variations exist between bottom electrode and dielectric, then fabrication can proceed, but poor grain growth and defects occur in MTJ
Solution Approach 1:
The conductive liner is deposited in advance to create a rigid, dishing-resistant surface. This preliminary structural reinforcement ensures that subsequent MTJ deposition occurs on a perfectly planar surface, enabling proper grain growth and defect-free fabrication
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
This approach results in a substantially flat and coplanar surface, reducing non-columnar grain growth and defectivity, thereby enhancing the formation of magnetic tunnel junctions with improved topography and reduced defects.
Implementation Method 1
depositing a conductive liner material in a recess of the recessed metal conductor
Implementation Method 2
depositing tantalum nitride in the recess on the conductive liner material
Implementation Method 3
polishing the tantalum nitride to the dielectric layer with a chemical mechanical planarization process
Data Source
AI summary
A substantially flat bottom electrode for magnetoresistive random access memory (MRAM) devices includes three components: a recessed bulk conductive material such as copper, a conductive liner lining the recess, and a cap layer, wherein the conductive liner is a harder material than the cap layer. The cap layer and the dielectric layer are coplanar having a height differential of less than 3 nanometers. The conductive liner has a lower chemical mechanical planarization removal rate. Also provided are processes for forming the bottom electrode.