MRAM MTJ Electrode Structure to Prevent Re-Sputtering Shorts
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Solution Overview
Problem
Reactive-ion etch and ion-beam etch processing of magneto-resistive random access memory (MRAM) devices leads to electrical shorts due to re-sputtering of thick bottom metal layers onto sidewalls of magnetic tunnel junction (MTJ) stacks, and results in high circular edge roughness, affecting device performance.
Innovation Solution
The use of an amorphous dielectric hardmask and a dielectric underlayer in conjunction with sidewall spacers to prevent metal re-sputtering, allowing for the simultaneous formation of top and bottom electrodes after MTJ stack patterning, thereby reducing the risk of electrical shorts and circular edge roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reactive-ion etch or ion-beam etch processing is used to pattern MTJ stacks, then the MTJ pillars can be formed, but electrical shorts occur due to re-sputtering of bottom metal layers onto sidewalls
Solution Approach 1:
A dielectric layer is introduced as an intermediary barrier between the bottom metal layer and the MTJ stack sidewalls. This dielectric layer prevents re-sputtered metal particles from creating electrical shorts while allowing the etch process to successfully pattern the MTJ pillars. The dielectric material acts as a protective mediator that resolves the conflict between achieving precise pillar formation and preventing electrical failures.
2Manufacturing precision
If polycrystalline metal hardmask is used for patterning, then the MTJ pillars can be defined, but defects are transferred into the pillars and circular edge roughness increases
Solution Approach 1:
The hardmask material parameter is changed from polycrystalline metal to amorphous dielectric material. This parameter change eliminates the grain boundary defects inherent in polycrystalline structures that would otherwise be transferred to the MTJ pillars during etching. The amorphous dielectric provides a defect-free masking layer that enables precise pillar definition without compromising device performance through defect transfer.
3Reliability
If thick bottom metal layers are used in the MTJ stack, then the magnetic storage function is achieved, but re-sputtering onto sidewalls causes electrical shorts
Solution Approach 1:
The dielectric layer serves as a protective intermediary that allows thick bottom metal layers to be used for achieving the required magnetic storage function without suffering from re-sputtering harm. The dielectric barrier physically separates the metal layer from the sidewalls, preventing metal particles from being deposited on insulating surfaces where they would create electrical shorts, thus enabling the use of thick metal layers safely.
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 decreases the risk of electrical shorts and increases device yield and reliability by forming MTJ pillars with reduced circular edge roughness and preventing metal re-sputtering, enhancing the performance of MRAM devices.
Implementation Method 1
Reactive-ion etch (RIE), and ion-beam etch (IBE) processing of such MTJ stacks presents a major challenge, as it typically leads to electrical shorts due to re-sputtering of underlying thick bottom metal layers onto MTJ stack sidewalls
Implementation Method 2
a first portion of a metal layer on opposite sidewalls of the amorphous dielectric hardmask, the first portion of the metal layer being in contact with a second portion of the uppermost surface of the magnetic tunnel junction pillar
Data Source
AI summary
A memory device includes a magnetic tunnel junction (MTJ) pillar between a top electrode and a bottom electrode. An amorphous dielectric hardmask is in contact with a first portion of an uppermost surface of the MTJ pillar. A first portion of a metal layer is disposed on opposite sidewalls of the amorphous dielectric hardmask and in contact with a second portion of the uppermost surface of the MTJ pillar extending outwards from the amorphous dielectric hardmask for providing the top electrode. A dielectric underlayer is in contact with a first portion of a bottommost surface of the MTJ pillar, while a second portion of the metal layer is disposed on opposite sidewalls of the dielectric underlayer. The second portion of the metal layer is in contact with a second portion of the bottommost surface of the MTJ pillar extending outwards from the dielectric underlayer for providing the bottom electrode.