T-Shaped Bottom Electrode for Etchless Sub-60 Nm MRAM
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Solution Overview
Problem
The fabrication of magnetoresistive random-access memory (MRAM) devices faces challenges in forming sub-60 nm magnetic tunneling junction (MTJ) structures due to chemical damage and metal re-deposition issues during reactive ion etching, which affects device performance.
Innovation Solution
A method involving high angle ion beam etching is used to create a T-shaped bottom electrode, allowing for the formation of sub-60 nm MTJ patterns without plasma etching, thereby avoiding chemical damage and metal re-deposition on the sidewalls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reactive ion etching (RIE) is used to pattern MTJ structures, then precise patterning and separation of MTJ cells is achieved, but chemical damage and metal re-deposition occur on the sidewalls, lowering device performance
Solution Approach 1:
The patent extracts and removes the harmful chemical components from the etching process by using pure physical ion beam etching instead of reactive ion etching. This eliminates the chemical damage and metal re-deposition issues while maintaining the patterning capability through physical sputtering mechanisms.
Solution Approach 2:
The patent changes the etching process parameters from chemical-dominated RIE to physical-dominated ion beam etching by adjusting ion energy, ion flux, and process chemistry. This parameter transformation allows precise patterning without the harmful chemical effects that occur in conventional RIE processes.
2Object-affected harmful factors
If ion beam etching (IBE) is used to avoid chemical damage, then sidewall damage is reduced, but conductive materials are re-deposited into the tunnel barrier, resulting in shorted devices
Solution Approach 1:
The patent converts the potentially harmful re-deposited metal materials into a beneficial protective layer by intentionally forming a sacrificial conductive layer that prevents tunnel barrier shorting. The re-deposited metal is redirected to serve as a protective barrier rather than a harmful contaminant.
Solution Approach 2:
The patent introduces an intermediary sacrificial conductive layer between the bottom electrode and the tunnel barrier. This intermediary layer acts as a mediator that captures re-deposited metal materials and prevents them from reaching and shorting the tunnel barrier, thus solving the re-deposition problem.
3Length of moving object
If conventional etching processes are used to form sub-60 nm MTJ structures, then device miniaturization is achieved, but device reliability deteriorates due to sidewall damage and shorting
Solution Approach 1:
The patent segments the bottom electrode into distinct regions with different heights (T-shaped structure), creating a stepped configuration that enables precise sub-60 nm patterning. This segmentation allows the formation of isolated MTJ cells with controlled dimensions while preventing the sidewall damage and shorting issues that plague conventional etching approaches.
Solution Approach 2:
The patent transitions from two-dimensional planar patterning to three-dimensional T-shaped electrode structures. By adding the vertical dimension with varying electrode heights, the patent achieves precise sub-60 nm lateral patterning control while maintaining device reliability through the protective geometry of the T-shaped structure.
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 enables the formation of electrically isolated MTJ patterns on a T-shaped bottom electrode, improving MRAM device performance by preventing chemical damage and metal re-deposition, thus enhancing the reliability of MRAM devices.
Implementation Method 1
pure physical etching techniques such as ion beam etching (IBE) have been applied to etch the MTJ stack to avoid the damaged MTJ sidewall
Implementation Method 2
Since the bottom portion is only sub 30 nm, much smaller than the top portion of sub 60 nm, the later MTJ deposition cannot form a continuous film along the electrode, but forms separate patterns on top
Data Source
AI summary
A first conductive layer is patterned and trimmed to form a sub 30 nm conductive via on a first bottom electrode. The conductive via is encapsulated with a first dielectric layer and planarized to expose a top surface of the conductive via. A second conductive layer is deposited over the first dielectric layer and the conductive via. The second conductive layer is patterned to form a sub 60 nm second conductive layer wherein the conductive via and second conductive layer together form a T-shaped second bottom electrode. MTJ stacks are deposited on the T-shaped second bottom electrode and on the first bottom electrode wherein the MTJ stacks are discontinuous. A second dielectric layer is deposited over the MTJ stacks and planarized to expose a top surface of the MTJ stack on the T-shaped second bottom electrode. A top electrode contacts the MTJ stack on the T-shaped second bottom electrode plug.