Patterning Semiconductor Film Stacks Without Etching MTJ Stacks
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Solution Overview
Problem
Conventional ion beam etching methods for fabricating magnetic tunnel junction (MTJ) stacks in MRAM devices cause damage, electrical short-circuits, and reduced yield due to sidewall re-deposition and sloping, making it difficult to pattern high-density MRAM devices effectively.
Innovation Solution
A method involving patterning a film stack with a buffer layer, oxide layer, dielectric capping layer, spin on carbon layer, and anti-reflective coating layer, etching to form a trench without the MTJ stacks present, depositing MTJ stacks, and then using chemical mechanical polishing to prevent sidewall damage and residues, thereby simplifying the patterning process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ion beam etching is used to pattern MTJ stacks, then patterning can be achieved, but sidewall re-deposition and sloping occur causing damage to MTJ stacks and electrical short-circuits
Solution Approach 1:
The patent applies preliminary action by forming the MTJ stacks before performing the etching process. The etching is performed on the underlying film stack structure (buffer layer, oxide layer, dielectric capping layer) before the MTJ stacks are deposited. This sequence prevents the etching process from directly contacting and damaging the MTJ stacks, eliminating sidewall re-deposition and sloping while maintaining patterning capability.
Solution Approach 2:
The patent segments the film stack into distinct layers with different etch selectivities. The dielectric capping layer and oxide layer are etched to form trenches, while the MTJ stacks remain intact due to their different material composition. This segmentation allows selective removal of certain layers while preserving the MTJ stacks, achieving patterning without damage.
2Ease of manufacture
If ion beam etching is used to pattern MTJ stacks, then patterning can be achieved, but residues are left on sidewalls causing electrical short-circuits
Solution Approach 1:
By performing etching before MTJ stack deposition, the patent eliminates the source of sidewall residues. The etching process acts on the underlying layers without generating residues on the MTJ stack sidewalls, as the MTJ stacks are not present during etching. This preliminary action sequence fundamentally removes the harmful effect of residue generation.
3Productivity
If ion beam etching is used to pattern high-density MRAM devices, then patterning can be achieved, but device thickness changes affect performance due to insufficient MTJ separation
Solution Approach 1:
The patent performs etching of the underlying film stack before MTJ stack deposition, establishing precise trench structures in advance. This preliminary action ensures that when MTJ stacks are deposited, they are positioned with accurate separation and uniform thickness, preventing the performance issues associated with insufficient separation in high-density devices.
Solution Approach 2:
The patent utilizes etch selectivity parameter changes to achieve precise patterning. By selecting etch conditions that preferentially etch the dielectric capping layer and oxide layer while leaving the MTJ stacks intact, the patent achieves precise control over MTJ stack separation and positioning, enabling high-density device fabrication with consistent performance.
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 prevents damage to MTJ stacks, eliminates sidewall residues, and facilitates easier patterning with consistent results, improving the yield and performance of MRAM devices by avoiding the challenges of ion beam etching.
Implementation Method 1
chemical mechanical polishing the film stack
Data Source
AI summary
One or more embodiments described herein generally relate to patterning semiconductor film stacks. Unlike in conventional embodiments, the film stacks herein are patterned without the need of etching the magnetic tunnel junction (MTJ) stack. Instead, the film stack is etched before the MTJ stack is deposited such that the spin on carbon layer and the anti-reflective coating layer are completely removed and a trench is formed within the dielectric capping layer and the oxide layer. Thereafter, MTJ stacks are deposited on the buffer layer and on the dielectric capping layer. An oxide capping layer is deposited such that it covers the MTJ stacks. An oxide fill layer is deposited over the oxide capping layer and the film stack is polished by chemical mechanical polishing (CMP). The embodiments described herein advantageously result in no damage to the MTJ stacks since etching is not required.