MTJ Bottom Electrode Width Reduction for Etching Damage Control
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Solution Overview
Problem
Current magnetic tunnel junction (MTJ) devices face challenges in etching processes, particularly at tight pitches, where ion beam etching (IBE) and chemical etching in reactive ion etching (RIE) lead to damage zones and metal redeposition, affecting tunnel magnetoresistance ratio and energy barrier variations, thus limiting downscaling in high-density MRAMs.
Innovation Solution
The solution involves reducing the width of the bottom electrode to be less than the MTJ stack pillar and embedding a metal seed layer within the bottom electrode to minimize metal redeposition during etching, thereby reducing the height of the MTJ stack pillar and avoiding over-etching of the bottom electrode, which helps in preventing metal shorts across the tunnel barrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ion beam etching (IBE) and chemical etching in reactive ion etching (RIE) are used to etch MTJ devices at tight pitches, then the etching process can be completed, but metal redeposition occurs on the MTJ stack pillar causing damage zones and affecting tunnel magnetoresistance ratio
Solution Approach 1:
The patent extracts the bottom electrode from the etching process by making it narrower than the MTJ stack pillar, so that the bottom electrode is not etched during the over-etching step. This prevents metal redeposition on the MTJ stack pillar while still completing the necessary etching of the MTJ stack and isolation structures.
Solution Approach 2:
The patent introduces a spacer layer as an intermediary between the bottom electrode and the MTJ stack pillar. The spacer layer protects the bottom electrode from etching and prevents metal redeposition, while allowing the etching process to complete the MTJ stack formation and isolation.
2Manufacturing precision
If the bottom electrode width is reduced to prevent metal redeposition, then tunnel barrier integrity is maintained, but the electrical connection area is reduced
Solution Approach 1:
The patent extracts the bottom electrode from the etching process by making it narrower, which maintains tunnel barrier integrity by preventing metal redeposition. The electrical connection area is sufficient for device operation while the narrower width prevents redeposition issues.
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 effectively reduces metal redeposition and etching damage, enhancing the reliability and scalability of MTJ devices by minimizing the redeposition of metal material during the etching process, thus maintaining the integrity of the tunnel barrier and improving the performance of MRAMs.
Implementation Method 1
ion beam etching (IBE)
Implementation Method 2
chemical etching in reactive ion etching (RIE)
Data Source
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AI summary
Aspects disclosed include reducing or avoiding metal deposition from etching magnetic tunnel junction (MTJ) devices. In one example, a width of a bottom electrode of an MTJ device is provided to be less than a width of the MTJ stack of the MTJ device. In this manner, etching of the bottom electrode may be reduced or avoided to reduce or avoid metal redeposition as a result of over-etching the MTJ device to avoid horizontal shorts between an adjacent device(s). In another example, a seed layer is embedded in a bottom electrode of the MTJ device. In this manner, the MTJ stack is reduced in height to reduce or avoid metal redeposition as a result of over-etching the MTJ device. In another example, an MTJ device includes an embedded seed layer in a bottom electrode which also has a width less than a width of the MTJ stack.