MTJ Pillar Etch via 90-Degree Rotation IBE
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Solution Overview
Problem
Current MTJ patterning methods, such as ion beam etching and chemical etching, face challenges in achieving vertical sidewall angles and preventing shorting between pillars, especially at tight pitches, due to shadowing and sidewall damage, which degrades magnetic tunnel junction properties.
Innovation Solution
A method involving sequential ion beam etching with 90-degree rotations of the MTJ device about a perpendicular axis to ensure uniform etching and minimize shadowing, allowing for the removal of horizontal surfaces and the formation of vertical sidewalls without chemical damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion beam etching is performed with uniform wafer rotation at 30 to 50 degree angle, then etching can be performed on MTJ structures, but shadowing of ion beam etching between pillars increases at tight pitch, making it difficult to achieve vertical sidewall angle and remove footings between pillars
Solution Approach 1:
The patent applies dynamic wafer rotation during the ion beam etching process, specifically rotating the wafer by 90 degrees between etching steps. This dynamic adjustment of the wafer orientation allows the ion beam to access different facets of the pillar structures, enabling the removal of horizontal surfaces and footings while maintaining vertical sidewalls. The rotation transforms a static etching process into a dynamic multi-angle process that overcomes the shadowing effect at tight pitches
Solution Approach 2:
The patent employs multiple sequential etching steps with wafer rotation to continuously remove material from different orientations. By performing repeated etching cycles with 90-degree rotations, the process continuously attacks horizontal surfaces and footings between pillars from various angles, ensuring complete removal without leaving residual material that would compromise vertical sidewall formation
2Productivity
If chemical etching in reactive ion etching is used, then etching can be performed on MTJ, but sidewall damage occurs due to oxygen or corrosive chemicals, resulting in degraded magnetic tunnel junction properties
Solution Approach 1:
The patent replaces chemical etching mechanisms with purely physical ion beam etching. By using accelerated ions to physically sputter material rather than relying on chemical reactions with oxygen or corrosive chemicals, the process eliminates chemical sidewall damage while maintaining effective etching capability. This mechanical/physical substitution preserves the integrity of the magnetic tunnel junction sidewalls
Solution Approach 2:
The ion beam etching process operates in a vacuum environment that is inherently inert and free from oxygen and corrosive chemicals. This inert atmosphere prevents oxidative damage and chemical corrosion of the MTJ sidewalls that would otherwise occur during reactive ion etching, while still allowing efficient material removal through ion bombardment
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 enhances etching efficiency and achieves improved sidewall profiles with reduced sidewall damage, enabling the fabrication of high-density MRAMs with improved magnetic tunnel junction properties.
Implementation Method 1
IBE involves directing a charged particle ion beam at a target material to etch the material
Implementation Method 2
IBE involves directing a charged particle ion beam at a target material to etch the material
Data Source
AI summary
Methods for MTJ patterning for a MTJ device are provided. For example, a method includes (a) providing an MTJ device comprising a substrate comprising a plurality of bottom electrodes, a MTJ layer disposed on the substrate, and a plurality of pillars disposed on the MTJ layer and over the plurality of bottom electrodes, wherein the plurality of pillars comprise a metal layer and a hard mask layer disposed on the metal layer, (b) conducting a first ion beam etching of the MTJ device; (c) rotating the MTJ device by 90 degrees in a clockwise or a counter clockwise direction about an axis perpendicular to a top surface of the MTJ device from a starting position; (d) conducting a second ion beam etching of the MTJ device; and (e) repeating steps (c) and (d).