MTJ Sidewall Protection via In-Situ Silicon Nitride Spacers
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Solution Overview
Problem
Conventional plasma etch methods for patterning magnetic tunnel junction (MTJ) stacks in spin-transfer torque MRAM devices suffer from leakage and short issues due to re-deposition of sputtered materials on sidewalls, and existing solutions are complex, requiring multiple machines and potentially degrading MTJ performance.
Innovation Solution
An in-situ sidewall protection layer comprising multiple silicon nitride spacers is formed during etching of the MTJ stack in a high-density plasma chemical vapor deposition (HDPCVD) chamber, providing protection to each sub-layer and preventing re-deposition of unwanted materials, thereby enhancing the patterning process without breaking vacuum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional plasma etch methods are used to pattern MTJ stacks, then the patterning process can be performed, but re-deposition of sputtered materials on sidewalls causes leakage and short issues
Solution Approach 1:
The patent applies preliminary action by forming sidewall protection layers (sidewall spacers) before the final etching step. These protection layers are deposited conformally on the sidewalls of MTJ sub-layers prior to etching, preventing re-deposition of sputtered materials during the etching process. This preliminary protective measure eliminates leakage and short issues while maintaining patterning precision.
Solution Approach 2:
The patent uses sidewall protection layers as intermediary structures between the etching plasma and the MTJ sidewalls. These protection layers act as mediators that intercept sputtered materials, preventing them from adhering to the MTJ sidewalls. The protection layers are subsequently removed, having served their protective function during etching.
2Loss of substance
If organic chemicals are added to argon plasma to reduce re-deposition, then volatility of by-products increases, but etch rate slows down and residual complexes impact MTJ long term reliability
Solution Approach 1:
The patent extracts the harmful organic chemicals from the etching process entirely. Instead of adding organic additives to argon plasma, the invention uses pure argon plasma with sidewall protection layers. This extraction eliminates the problem of residual organometallic complexes that would otherwise impact MTJ long term reliability, while still achieving high by-product volatility through the physical sputtering mechanism.
3Reliability
If multiple machines are used for etching and sidewall protection, then sidewall protection can be achieved, but process complexity increases and requires different machines or tools
Solution Approach 1:
The patent merges multiple processes into a single HDPCVD chamber by integrating sidewall protection layer deposition and removal steps with the etching process. The protection layers are deposited and removed within the same chamber using sequential deposition and etching cycles, eliminating the need for multiple separate machines and reducing process complexity while maintaining effective sidewall protection.
Solution Approach 2:
The HDPCVD chamber is used for multiple functions: depositing the sidewall protection layers, performing the main etching process, and removing the protection layers. This multi-functional use of a single chamber eliminates the need for specialized separate equipment for each step, reducing overall process complexity while achieving comprehensive sidewall protection.
4Reliability
If conventional multi-step process with different machines is used, then sidewall protection can be achieved, but manufacturing time and cost increase
Solution Approach 1:
The patent combines sidewall protection layer deposition, main etching, and protection layer removal into a single continuous process within one HDPCVD chamber. By merging these previously separate steps into one integrated sequence, the manufacturing time is reduced and throughput is improved, while maintaining reliable sidewall protection throughout the process.
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 effectively prevents leakage and short issues, improving MTJ performance by maintaining the integrity of the sidewall protection and reducing the complexity and cost of the fabrication process, while maintaining high throughput.
Implementation Method 1
An in-situ sidewall protection layer comprising multiple silicon nitride spacers is formed during etching of the MTJ stack in a high-density plasma chemical vapor deposition (HDPCVD) chamber
Implementation Method 2
high-density plasma chemical vapor deposition (HDPCVD) chamber
Data Source
AI summary
A magnetic memory device includes an MTJ element between a bottom electrode layer and a top electrode layer. The MTJ element comprises a reference layer, a tunnel barrier layer and a free layer. The reference layer comprises sub-layers that protrude beyond a sidewall of the tunnel barrier layer. The tunnel barrier layer protrudes beyond a sidewall of one of sub-layers of the free layer. Sidewall spacers are disposed to respectively cover a sidewall of the top electrode layer, sidewalls of the sub-layers of the free layer, a sidewall of the tunnel barrier layer, and sidewalls of the sub-layers of the reference layer. The etching of the MTJ stack and the formation of the sidewall spacers are carried out in the same HDPCVD chamber without breaking the vacuum.