Undercut Via Electrode for Etchless Sub-60 Nm MRAM MTJ Patterning
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Solution Overview
Problem
The fabrication of magnetoresistive random-access memory (MRAM) devices involves precise patterning steps, including reactive ion etching (RIE), which can cause sidewall damage and re-deposition of metal materials in magnetic tunneling junctions (MTJ), leading to device performance issues.
Innovation Solution
A method for forming MTJ structures without chemical damage or re-deposition of metal materials, involving the deposition of a first dielectric layer on a bottom electrode, partial etching to form a via opening with straight sidewalls, and subsequent etching to create a tapered via opening, allowing for the formation of MTJ patterns on an undercut via electrode without etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reactive ion etching (RIE) is used to pattern MTJ cells, then precise patterning and separation of MTJ cells is achieved, but sidewall damage occurs and device performance deteriorates
Solution Approach 1:
The patent extracts and removes the harmful plasma etching step from the fabrication process. Instead of using RIE to pattern the MTJ stack, the invention uses a lift-off process where a sacrificial layer is removed, allowing the MTJ stack to be formed and then released without exposure to plasma, thereby eliminating sidewall damage while maintaining patterning precision through controlled deposition and lift-off geometry
Solution Approach 2:
The patent replaces the chemical-mechanical plasma etching system with a purely physical deposition and lift-off system. The patterning is achieved through controlled material deposition followed by mechanical or chemical removal of a sacrificial layer, substituting the harmful plasma field with a gentler physical process that avoids sidewall erosion and charging effects
2Object-affected harmful factors
If ion beam etching (IBE) is used to etch the MTJ stack, then sidewall damage is avoided, but conductive materials are re-deposited into the tunnel barrier causing device shorts
Solution Approach 1:
The patent extracts and eliminates the IBE step from the process flow. Instead of using ion beam etching to create the MTJ pattern, the invention employs a deposition-based lift-off process where materials are deposited conformally and then released by removing a sacrificial layer, completely removing the source of metal re-deposition that causes tunnel barrier shorts
Solution Approach 2:
The patent substitutes the physical sputtering and ion beam removal process with a controlled deposition and sacrificial layer release process. This replaces the mechanism that causes metal re-deposition with a process where materials are deposited in a controlled manner and then cleanly removed via lift-off, preventing contamination of the tunnel barrier while maintaining the desired MTJ pattern
3Ease of manufacture
If plasma etching is used to form MTJ patterns, then material removal is achieved, but chemical damage and metal re-deposition occur on MTJ sidewalls
Solution Approach 1:
The patent extracts and removes the plasma etching step entirely from the fabrication sequence. The material removal function is replaced by a lift-off process where a sacrificial layer is deposited, the MTJ stack is formed on top, and then the sacrificial layer is removed, achieving the desired pattern without exposing the MTJ sidewalls to plasma chemistry that causes damage and re-deposition
Solution Approach 2:
The patent introduces a sacrificial layer as an intermediary element in the fabrication process. This sacrificial layer serves as a temporary placeholder that enables controlled deposition of the MTJ stack and is subsequently removed to create the final pattern, acting as a mediator that eliminates the need for direct plasma etching of the MTJ materials and their associated harmful effects
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 avoids chemical damage and metal re-deposition on MTJ sidewalls, improving the performance of MRAM devices by enabling the formation of sub-60 nm MTJ patterns without plasma etching.
Implementation Method 1
A first dielectric layer is deposited on a bottom electrode
Implementation Method 2
precise patterning steps including reactive ion etching (RIE) are usually involved. During RIE, high energy ions remove materials vertically
Implementation Method 3
A metal layer is deposited over the first dielectric layer and in the second via opening
Data Source
AI summary
A method for fabricating a magnetic tunneling junction (MTJ) structure is described. A first dielectric layer is deposited on a bottom electrode and partially etched through to form a first via opening having straight sidewalls, then etched all the way through to the bottom electrode to form a second via opening having tapered sidewalls. A metal layer is deposited in the second via opening and planarized to the level of the first dielectric layer. The remaining first dielectric layer is removed leaving an electrode plug on the bottom electrode. MTJ stacks are deposited on the electrode plug and on the bottom electrode wherein the MTJ stacks are discontinuous. A second dielectric layer is deposited over the MTJ stacks and polished to expose a top surface of the MTJ stack on the electrode plug. A top electrode layer is deposited to complete the MTJ structure.