MRAM Tunnel Barrier Raised Edge to Prevent MTJ Sidewall Shorts
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Solution Overview
Problem
The existing etching processes for forming magnetoresistive random-access memory (MRAM) devices often result in re-sputtering effects, causing metal elements from the bottom electrode layer to redeposit onto the sidewall surfaces of ferromagnetic layers and tunnel barrier layers, leading to shorts between otherwise isolated layers.
Innovation Solution
The proposed solution involves a method of forming a MRAM structure with a magnetic tunnel junction (MTJ) stack that includes a bottom electrode layer, a first ferromagnetic layer, a tunnel barrier layer, and a top electrode layer, where the second ferromagnetic layer is directly on top of the tunnel barrier layer with angled sidewalls, and a peripheral portion of the tunnel barrier layer surrounds the sidewall of the second ferromagnetic layer, along with the use of a metal hard mask layer and anisotropic etching to prevent re-sputtering and shorts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching processes (RIE/IBE) are used to form the MTJ stack, then the vertical MTJ stack can be formed through blanket layer patterning, but re-sputtering effect causes metal elements to redeposit onto sidewall surfaces, resulting in shorts between ferromagnetic layers
Solution Approach 1:
A peripheral portion of the tunnel barrier layer is formed to extend over the sidewall of the second ferromagnetic layer before the etching process occurs. This preliminary structural preparation creates a protective barrier that prevents metal elements from redepositing onto the sidewall surfaces during subsequent etching operations, thereby preventing shorts between ferromagnetic layers
Solution Approach 2:
The peripheral portion of the tunnel barrier layer acts as an intermediary protective structure between the bottom electrode layer and the second ferromagnetic layer. This intermediate structure intercepts and blocks the re-sputtered metal elements, preventing them from reaching and creating conductive paths between the ferromagnetic layers
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 shorts between ferromagnetic layers by creating an obtuse angle between the sidewalls of the second ferromagnetic layer and the bottom surface, allowing for improved isolation and preventing re-sputtering, thus enhancing the reliability and integrity of the MRAM structure.
Implementation Method 1
such etching process may sometimes come with re-sputtering effect, which causes metal elements from, for example, the blanket bottom electrode layer to be re-deposited onto sidewall surfaces of the ferromagnetic layers and/or the tunnel barrier layer
Data Source
AI summary
Embodiments of present invention provide a method of forming a MRAM structure. The method includes patterning a bottom electrode layer and a first ferromagnetic layer on top of the bottom electrode layer; depositing a dielectric layer, the dielectric layer covering the bottom electrode layer and the first ferromagnetic layer; creating an opening in the dielectric layer, the opening exposing a portion of the first ferromagnetic layer; forming a tunnel barrier layer inside the opening; forming a second ferromagnetic layer on top of the tunnel barrier layer; patterning the tunnel barrier layer and the second ferromagnetic layer; and forming a top electrode layer on top of the second ferromagnetic layer. Structures formed thereby are also provided.