MRAM MTJ Stack Formation with Spacer Layers
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Solution Overview
Problem
Current magnetoresistive random access memory (MRAM) devices face challenges in preventing defects and reducing leakage current due to etching processes, particularly when using chlorine etchants, which can damage the TiN top electrode and affect data retention.
Innovation Solution
The formation of a magnetic tunnel junction (MTJ) stack within a substrate, involving a bottom electrode, a MTJ layer stack with a pinned and free ferromagnetic layer, and a titanium-containing top electrode, along with spacer layers to reduce critical dimensions and prevent damage from etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chlorine etchants are used in etching processes, then etching effectiveness is improved, but damage to TiN top electrode and leakage current increase
Solution Approach 1:
A spacer layer is introduced as an intermediary between the chlorine etchant and the TiN top electrode. The spacer layer is selectively removed to expose the MTJ stack for etching while protecting the TiN electrode from direct contact with the harmful etchant, thus maintaining etching effectiveness while preventing electrode damage and leakage current
Solution Approach 2:
The spacer layer is formed beforehand to prevent damage to the TiN top electrode before the etching process occurs. This preliminary protective action blocks the harmful chlorine etchant from reaching the electrode, thereby preventing leakage current and maintaining data retention while still allowing the etching process to proceed effectively on the MTJ stack
2Ease of manufacture
If etching processes are performed to form MTJ stack, then device structure is created, but defects and leakage current are generated
Solution Approach 1:
The spacer layer serves as a protective intermediary that enables the etching process to proceed while preventing defects. By selectively removing the spacer layer in controlled regions, the MTJ stack can be etched with high precision while the TiN electrode remains protected from damage that would cause defects
Solution Approach 2:
The spacer layer is selectively removed in specific regions to expose the MTJ stack for etching while leaving it intact in other regions to protect the TiN electrode. This segmentation approach allows the etching process to create the desired device structure without generating defects from uncontrolled etchant exposure
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 minimizes defects and leakage current, enhances data retention, and reduces the risk of damage from etching by-products, thereby improving the reliability and performance of MRAM devices.
Implementation Method 1
The tunnel barrier layer is thin enough (such a few nanometers) to permit electrons to tunnel from one ferromagnetic layer to the other
Implementation Method 2
A resistance of the MTJ stack is adjusted by changing a direction of a magnetic moment of the ferromagnetic free layer with respect to that of the ferromagnetic pinned layer
Data Source
AI summary
A method of forming a magnetic random access memory (MRAM) device includes forming a bottom electrode layer over a substrate including an inter-metal dielectric (IMD) layer having a metal line therein; forming a barrier layer over the bottom electrode layer; forming a magnetic tunnel junction (MTJ) layer stack over the bottom electrode layer; forming a dielectric layer over the MTJ layer stack; forming an opening in the dielectric layer to expose the barrier layer; filling the opening in the dielectric layer with a top electrode; after filling the opening in the dielectric layer with the top electrode, etching the dielectric layer to expose the barrier layer; and patterning the MTJ layer stack to form an MTJ stack that exposes the bottom electrode layer.