MRAM MTJ Spacer Structure for Preserving Top Electrode Height
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Solution Overview
Problem
The fabrication of MRAM cells faces challenges due to the reduction in height of top electrodes during 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 from 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 the bottom electrode layer, then the MTJ stack and top electrode are laterally surrounded by sidewall spacers, but the top electrode height is reduced and the landing window for metal lines is narrowed
Solution Approach 1:
The patent applies preliminary action by forming a protective mask layer over the top electrode before the spacer etching process. This mask layer is deposited in advance to prevent the top electrode from being etched away during the self-aligned spacer formation process, thereby preserving the top electrode height while still enabling precise sidewall spacer alignment.
Solution Approach 2:
The patent introduces an intermediary protective mask layer that acts as a mediator between the spacer etching process and the top electrode. This intermediate layer allows the etching to proceed for forming precise sidewall spacers while protecting the top electrode from excessive etching, thus resolving the contradiction between alignment precision and top electrode height preservation.
2Manufacturing precision
If self-aligned spacer etching is performed to form sidewall spacers, then lateral surrounding structure is created, but susceptibility to damage during trench etching increases
Solution Approach 1:
The protective mask layer is formed in advance before the trench etching process. This preliminary protective structure ensures that when trench etching is performed later, the top electrode is already protected and cannot be damaged, while still allowing the self-aligned sidewall spacers to be formed with high precision in the earlier stage.
Solution Approach 2:
The patent applies beforehand cushioning by depositing the protective mask layer that acts as a cushion or buffer between the harmful trench etching process and the vulnerable top electrode. This prior protective measure ensures that even if the trench etching process is aggressive, the top electrode remains protected and maintains its structural integrity.
3Manufacturing precision
If additional etch stop layer and photolithography process are added to protect top electrodes, then landing window stability is improved, but fabrication process complexity increases
Solution Approach 1:
The protective mask layer serves a dual function: it protects the top electrode during spacer etching and also serves as an etch stop layer during subsequent trench etching. This self-service approach means one additional process step provides multiple protective functions, reducing the net increase in process complexity while maintaining landing window stability.
Solution Approach 2:
The patent makes the protective mask layer multi-functional by having it serve both as a protection layer during spacer formation and as an etch stop layer during trench etching. This universality means that instead of adding separate protective measures for each process step, a single additional layer provides protection across multiple stages, thereby limiting the increase in fabrication complexity.
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.