STT-MRAM MTJ Formation via Additive Template Deposition
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Solution Overview
Problem
The manufacturing of Magnetoresistive Random-Access Memory (MRAM) devices is hindered by the difficulty in controlling the etching of multiple metal layers, leading to electrical shorting and non-uniformity issues in Magnetic Tunnel Junctions (MTJs), which limits the commercialization of MRAM devices.
Innovation Solution
An additive method is introduced using a pre-patterned template to deposit metal layers anisotropically, minimizing overlap and shorting by filtering out isotropic metal ions through Physical Vapor Deposition (PVD) techniques, allowing for self-collimated and self-aligned formation of MTJ cells without subtractive processing like plasma etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional subtractive etching techniques are used to form MTJ structures, then metal layers can be removed to create patterns, but etching residue causes electrical shorting and non-uniformity across the substrate
Solution Approach 1:
The patent inverts the traditional subtractive etching approach by using additive deposition through a pre-patterned template. Instead of removing material to form patterns, metal layers are deposited only where needed through template apertures, eliminating etching residue and the associated shorting defects while improving uniformity across the substrate
Solution Approach 2:
A pre-patterned template serves as an intermediary structure during metal layer deposition. The template with controlled apertures directs the metal flux, enabling precise pattern formation without direct contact between the deposition source and substrate, thereby preventing residue formation and ensuring uniform MTJ layer quality
2Ease of manufacture
If multiple metal layers are etched to form MTJ structure, then the MTJ can be created, but multi-step etching introduces sidewall modifications that degrade storage capability
Solution Approach 1:
The patent replaces multi-step subtractive etching with a single additive deposition step through a pre-patterned template. This inversion eliminates repeated sidewall exposure and modification during multiple etching steps, preserving the integrity of metal layer sidewalls and maintaining storage capability while still achieving MTJ structure formation
3Quantity of substance
If PVD deposition is performed without a template, then metal layers are deposited isotropically, but this causes overlap and shorting between layers
Solution Approach 1:
A pre-patterned template acts as an intermediary that converts isotropic PVD deposition into anisotropic layer formation. The template apertures physically constrain the metal flux, ensuring deposition occurs only in intended locations with proper layer separation, preventing overlap and shorting while maintaining efficient material utilization
Solution Approach 2:
The pre-patterned template creates local quality variations in the deposited metal layers by providing aperture patterns that control where metal is deposited. Different regions of the substrate receive metal deposition selectively through the template apertures, ensuring proper spatial separation and alignment of metal layers while preventing unwanted overlap
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 reduces metal etch process steps, enhances uniformity and sidewall profiles of the MTJ structure, thereby improving the performance and reliability of MRAM devices by preventing electrical shorting and maintaining storage capability.
Implementation Method 1
depositing metal layers through a pre-patterned template to form a MTJ structure by skimming away portions of the PVD metal flux that would prevent anisotropic deposition on a underlying substrate
Implementation Method 2
achieving an anisotropic deposition result by skimming away metal ions that would prevent collimated layers from forming on the substrate
Data Source
AI summary
Methods for additive formation of a STT-MRAM metal stack using a deposition process through a pre-patterned template that skims away metal ions that are less likely to enable anisotropic deposition on a substrate. The pre-patterned template is formed from a film stack using patterning techniques to form an opening in the film stack that exposes portions of an underlying substrate where a MTJ will be formed for an MRAM cell. The film stack cavity may be exposed to etch processes that selectively pull back the sidewall, such that other layers in the film stack protrude into the cavity. Additional treatments to the other layers may alter the opening sizes in the other layers. Metal deposited through the cavity such that metal ions with anisotropic characteristics will be skimmed away before reaching the substrate.