MRAM Bottom Electrode Etching with Conformal Dielectric Protection
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Solution Overview
Problem
Current MRAM fabrication processes face challenges such as bottom electrode (BE)-BE shorts, BE-bit line shorts, and damage to magnetic tunnel junction (MTJ) sidewalls during etching and cleaning steps, which limit device yield and performance.
Innovation Solution
A method involving a conformal dielectric layer, a bottom anti-reflection coating (BARC), and a photoresist layer is used to protect MTJ layers during patterning, with a wet-dry-wet stripping sequence to remove residues and prevent shorts, and a controlled overetch to ensure complete removal of BE residues, while using a dielectric anti-reflective coating or spin-on hard masks for enhanced anti-reflective properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional etching and cleaning steps are used during MRAM fabrication, then manufacturing process simplicity is maintained, but bottom electrode-BE shorts, BE-bit line shorts, and MTJ sidewall damage occur
Solution Approach 1:
A conformal dielectric layer is deposited over the MTJ stack before bottom electrode patterning to protect the MTJ sidewalls from etching damage and residue formation. This preliminary protective action prevents shorts and damage during subsequent etching and cleaning steps, directly improving device yield without requiring complex post-processing repairs
Solution Approach 2:
The fabrication process is segmented into distinct protected zones: the MTJ stack is isolated by the conformal dielectric layer, while the bottom electrode is patterned in exposed regions. This segmentation allows different process conditions to be applied to different areas, enabling complete BE residue removal through overetching while protecting the MTJ sidewalls from damage
2Reliability
If overetching is performed to remove BE residues, then BE-BE shorts and BE-bit line shorts are prevented, but MTJ sidewalls may be damaged
Solution Approach 1:
The conformal dielectric layer serves as a cushioning protective barrier deposited beforehand over the MTJ stack. This layer absorbs the harmful effects of overetching, allowing aggressive etching conditions to be used for complete bottom electrode residue removal while the dielectric layer prevents direct plasma exposure and damage to the MTJ sidewalls
3Reliability
If aggressive cleaning steps are used to remove residues, then shorting is prevented, but MTJ layers are damaged
Solution Approach 1:
The conformal dielectric layer acts as an intermediary protective barrier between the aggressive cleaning/etching processes and the sensitive MTJ layers. This intermediate layer can withstand harsh cleaning conditions while protecting the underlying MTJ stack, enabling complete residue removal without direct exposure of the MTJ layers to damaging chemicals or plasma
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 eliminates BE-BE and BE-bit line shorts, protects MTJ sidewalls, and improves device yield by ensuring thorough residue removal without damaging underlying layers, enabling the production of high-density MRAM devices.
Implementation Method 1
a conformal dielectric layer is deposited on the array of MTJ cells to protect the MTJ layers therein from subsequent plasma and wet process steps
Implementation Method 2
A bottom anti-reflection coating (BARC) and a photoresist layer are sequentially formed on the protective dielectric layer
Implementation Method 3
a wet-dry-wet stripping sequence to remove residues and prevent shorts
Implementation Method 4
a wet-dry-wet stripping sequence
Implementation Method 5
a controlled overetch to ensure complete removal of BE residues
Implementation Method 6
using a dielectric anti-reflective coating or spin-on hard masks for enhanced anti-reflective properties
Data Source
AI summary
A BE patterning scheme in a MRAM is disclosed that avoids damage to the MTJ array and underlying ILD layer while reducing BE-BE shorts and BE-bit line shorts. A protective dielectric layer is coated over a MTJ array before a photoresist layer is coated and patterned on the dielectric layer. The photoresist pattern is transferred through the dielectric layer with a dielectric etch process and then through the BE layer with a metal etch that includes a certain amount of overetch to remove metal residues. The photoresist is stripped with a sequence involving immersion or spraying with an organic solution followed by oxygen ashing to remove any other organic materials. Finally, a second wet strip is performed with a water based solution to provide a residue free substrate. In another embodiment, a bottom anti-reflective coating (BARC) is inserted between the photoresist and dielectric layer for improved critical dimension control.