Self-Aligned MRAM Bottom Electrode Structure to Prevent MTJ Shorts
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Solution Overview
Problem
In the fabrication of magnetic tunnel junction (MTJ) devices, the use of reactive ion etch and ion beam etch processes often leads to shorts due to re-sputtering of thick bottom metal layers, which complicates the formation of well-defined interfaces essential for high-performance MRAM devices.
Innovation Solution
A self-aligned bottom electrode is formed with a metal-oxide structure, where a metal layer is surrounded by an oxide to prevent re-sputtering, using techniques such as high temperature deposition of titanium to form titanium dioxide, which acts as a dielectric and avoids shorts during MTJ stack patterning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional patterning methods are used for MTJ structures, then manufacturing process is simpler, but metal re-sputtering causes shorts between layers
Solution Approach 1:
The bottom electrode is formed with self-alignment to the MTJ stack before patterning occurs. This preliminary structuring ensures that the bottom electrode maintains its lateral dimensions and remains surrounded by oxide during subsequent patterning steps, preventing metal re-sputtering and shorts between layers while maintaining manufacturing feasibility
Solution Approach 2:
An oxide layer is introduced as an intermediary material surrounding the bottom electrode. This oxide acts as a protective barrier that prevents direct exposure of the bottom electrode during patterning, thereby preventing metal re-sputtering and shorts while allowing the patterning process to proceed with conventional methods
2Ease of manufacture
If bottom electrode is exposed during patterning, then manufacturing is easier, but lateral dimensions change and shorts occur
Solution Approach 1:
The bottom electrode is pre-formed with self-alignment to the MTJ stack, establishing precise lateral dimensions before patterning. This preliminary structuring allows the electrode to maintain its dimensions throughout subsequent processing without requiring complex protection steps
Solution Approach 2:
The surrounding oxide layer serves as an intermediary protective structure that maintains the bottom electrode's lateral dimensions during patterning. The oxide prevents direct exposure and dimensional changes while allowing conventional patterning methods to be used
3Manufacturing precision
If metal spacer is used for self-alignment, then bottom electrode alignment improves, but additional fabrication steps are required
Solution Approach 1:
The metal spacer is formed in advance as a self-aligned structure that defines the lateral dimensions and position of the bottom electrode. This preliminary structuring establishes precise alignment without requiring additional alignment steps during subsequent processing
Solution Approach 2:
The metal spacer serves a dual function: it acts as both a structural element and a self-aligned mask for bottom electrode formation. The spacer automatically defines the electrode's position and dimensions through its own geometry, eliminating the need for separate alignment procedures
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 the risk of shorts between layers, ensuring well-defined interfaces and improving the reliability of MTJ structures by preventing metal re-sputtering, thus enhancing the performance of MRAM devices.
Implementation Method 1
forming a metal layer on the metal spacer and dielectric with a high temperature deposition of the metal layer, where the metal layer oxidizes
Data Source
AI summary
A magnetic tunnel junction (MTJ) stack, where a vertical side surface of a bottom electrode of the MTJ stack is surrounded by an oxide, where the bottom electrode and the oxide are horizontally aligned. A magnetic tunnel junction (MTJ) stack, where a vertical side surface of a bottom electrode of the MTJ stack and a metal spacer below the bottom electrode is surrounded by an oxide, where an upper surface of the bottom electrode is horizontally aligned with a horizontal upper surface of the oxide, where a lower surface of the metal spacer is horizontally aligned with a horizontal lower surface of the oxide. Forming a metal spacer above and vertically aligned with a lower metal line surrounded by a dielectric, and forming a metal layer on the metal spacer and dielectric with a high temperature deposition of the metal layer, where the metal layer oxidizes.