MTJ Memory Cell Spacer Etching to Preserve Top Electrode Height
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Solution Overview
Problem
The challenge in MRAM cell fabrication is the reduction in height of top electrodes due to self-aligned spacer etching, which narrows the landing window for metal lines and increases susceptibility to damage during trench etching.
Innovation Solution
Implementing an additional etch stop layer and a photolithography process to protect top electrodes during etching, along with a self-aligned spacer etching process that stops before patterning the bottom electrode layer, ensuring a relaxed landing window for metal lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If self-aligned spacer etching is performed to pattern bottom electrodes, then manufacturing precision is improved, but top electrode height is reduced
Solution Approach 1:
The etching process is segmented into two distinct stages: first etching the spacer layer to form sidewall spacers, then etching the bottom electrode layer. This segmentation prevents the top electrode from being etched away while still achieving precise patterning of the bottom electrode through the self-aligned spacer mechanism.
Solution Approach 2:
The spacer layer is deposited and etched in advance before the bottom electrode patterning step. This preliminary action creates the self-aligned sidewall spacers that define the precise location for subsequent bottom electrode formation, while preserving the top electrode height for the landing window.
2Manufacturing precision
If top electrode height is reduced, then manufacturing precision is improved, but reliability deteriorates
Solution Approach 1:
By separating the etching of the spacer layer from the etching of the bottom electrode layer, the process maintains adequate top electrode height for structural integrity while still achieving the precision needed for the landing window through the self-aligned spacer definition.
Solution Approach 2:
The spacer layer acts as an intermediary element that enables precise alignment without requiring excessive etching of the top electrode. The sidewall spacers formed from the spacer layer serve as the actual alignment reference for the landing window, mediating between the top and bottom electrodes.
3Manufacturing precision
If self-aligned spacer etching is performed, then manufacturing precision is improved, but susceptibility to damage increases
Solution Approach 1:
The etching process is divided into two separate steps: first etching only the spacer layer to form sidewall spacers, then etching the bottom electrode layer. This segmentation ensures the top electrode is not exposed to etching damage while still achieving precise pattern alignment through the self-aligned spacer mechanism.
Data Source
AI summary
A memory device includes a bottom electrode, a magnetic tunnel junction (MTJ) stack, a top electrode, and a sidewall spacer. The MTJ stack is over the bottom electrode. The top electrode is over the MTJ stack. The sidewall spacer laterally surrounds the MTJ stack and the top electrode. The sidewall spacer has an outermost sidewall laterally set back from an outermost sidewall of the bottom electrode.