MTJ Pillar Formation Using Two-Step Etching for MRAM Reliability
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Solution Overview
Problem
Current MRAM MTJ pillar formation requires aggressive IBE etching to remove metal residues, which causes shorts due to gouging into the NBLOK and exposes Cu, leading to oxidation and loss, while mild IBE results in significant MTJ sidewall damage.
Innovation Solution
A two-step etching process involving a first etch to form MTJ pillars with a spacer and a second etch with smaller openings, using different dielectric layers to minimize NBLOK loss and protect the underlying structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If aggressive IBE etching is used to remove metal residues, then metal residue removal is improved, but NBLOK loss and Cu exposure occur
Solution Approach 1:
The patent segments the etching process into multiple steps with different opening sizes. The first etching step uses a larger opening to remove bulk metal residues, while the second step uses a smaller opening to perform targeted cleaning without excessive NBLOK loss. This segmentation allows each step to be optimized for its specific function, resolving the contradiction between thorough residue removal and NBLOK preservation.
Solution Approach 2:
The patent performs preliminary removal of the majority of metal residues in the first etching step before performing the final cleaning in the second step. This preliminary action reduces the burden on the second step, allowing it to use a smaller opening that minimizes NBLOK loss while still achieving complete residue removal.
2Reliability
If mild IBE is used to avoid NBLOK loss, then NBLOK integrity is improved, but MTJ sidewall damage increases
Solution Approach 1:
The patent divides the etching process into two segmented steps where the first step uses a larger opening for bulk material removal and the second step uses a smaller opening for precise sidewall cleaning. This segmentation allows the process to achieve both NBLOK preservation and MTJ sidewall quality without requiring a single compromised opening size.
Solution Approach 2:
The patent changes the etching parameters (opening size) between steps. The first step uses a larger opening parameter to remove bulk residues efficiently, while the second step uses a smaller opening parameter to clean sidewalls gently. This parameter change allows optimization for different functions at different stages, resolving the contradiction between NBLOK protection and sidewall quality.
3Productivity
If large IBE opening is used during pillar formation, then etching efficiency is improved, but NBLOK loss due to loading effect increases
Solution Approach 1:
The patent segments the etching operation into two phases: a first phase with a larger opening that achieves high etching efficiency for bulk removal, and a second phase with a smaller opening that minimizes NBLOK loss during final cleaning. This segmentation resolves the contradiction by allowing each phase to be optimized for its specific objective without compromising the other.
Solution Approach 2:
The first etching step performs the preliminary bulk removal of metal residues using a large opening, achieving high etching efficiency. This preliminary action reduces the amount of material remaining, allowing the second step to use a smaller opening that minimizes NBLOK loss while completing the cleaning process.
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
The method effectively forms MTJ pillars with minimal NBLOK loss and reduced sidewall damage, ensuring reliable MRAM device integrity by using a two-step etching process with selective dielectric layers.
Implementation Method 1
Current MRAM MTJ pillar formation requires aggressive IBE etch to remove the metal residues on the MTJ sidewall
Implementation Method 2
a post etching oxidation to oxidize the metal residues will introduce significant MTJ sidewall damage
Data Source
AI summary
A method of manufacturing an MRAM device includes forming an MTJ stack on a substrate, forming a hardmask layer on the MTJ stack, forming etch pattern pads on the hardmask, forming a spacer on the sides of the etch pattern pads to form first openings exposing the hardmask, patterning the MTJ stack by a first etch using the first openings to form a plurality of first MTJ pillars separated by first vias, filling the first vias with a first dielectric, removing the spacers from the etch pattern pads to form a plurality of second openings between the first dielectric and the etch pattern pads, patterning the plurality of first MTJ pillars by a second etch using the second openings to form a plurality of second MTJ pillars separated by second vias and filling the second vias with a second dielectric to encapsulate the plurality of second MTJ pillars.