T-Shaped MRAM Ferromagnetic Layer for MTJ Sidewall Isolation
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Solution Overview
Problem
The existing etching processes for forming magnetic tunnel junction (MTJ) stacks in MRAM devices often result in re-sputtering effects, leading to shorts between ferromagnetic layers due to the redeposition of metal elements from the bottom electrode layer onto the sidewall surfaces, which compromises the isolation provided by the tunnel barrier layer.
Innovation Solution
Incorporating a silicon-carbon-nitride (SiCN) dielectric layer between the bottom electrode layer and the first ferromagnetic layer, with an etch-stop layer to prevent re-sputtering and ensure proper patterning of the MTJ stack, including the use of a metal hard mask for anisotropic etching that stops at the etch-stop layer, thereby avoiding shorts between the ferromagnetic layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reactive ion etching (RIE) and/or ion beam etching (IBE) processes are used to etch the stack of blanket layers, then the vertical MTJ stack can be formed, but metal elements from the bottom electrode layer are re-deposited onto sidewall surfaces of the ferromagnetic layers and/or tunnel barrier layer, resulting in shorts between the two ferromagnetic layers
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the bottom electrode layer and the ferromagnetic layers. This dielectric layer acts as a barrier that prevents metal elements from the bottom electrode from being re-deposited onto the ferromagnetic layers during etching, thereby eliminating shorts while allowing the etching process to proceed effectively
Solution Approach 2:
The structure is segmented into distinct functional layers with the dielectric layer positioned specifically between the bottom electrode and ferromagnetic layers. This segmentation isolates the problematic interaction zone and allows each layer to perform its intended function without interfering with adjacent 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 prevents re-sputtering and ensures reliable isolation between the ferromagnetic layers, enhancing the structural integrity and operational reliability of the MRAM device by maintaining the integrity of the tunnel barrier layer and preventing unwanted shorts.
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 forming a bottom electrode layer surrounded by a bottom dielectric layer; forming an etch-stop layer on top of the bottom electrode layer and the bottom dielectric layer; creating an opening in the etch-stop layer to expose a top surface of the bottom electrode layer; forming a first ferromagnetic layer on top of the bottom electrode layer and the etch-stop layer, with a portion of the first ferromagnetic layer filling the opening in the etch-stop layer; forming a tunnel barrier layer and a second ferromagnetic layer on top of the first ferromagnetic layer; patterning the second ferromagnetic layer, the tunnel barrier layer, and the first ferromagnetic layer; and forming a top electrode layer on top of the second ferromagnetic layer. A structure formed thereby is also provided.