Multi-Step Ion Beam Etch for Magnetic Sensor Sidewall Trimming
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Solution Overview
Problem
Existing methods fail to reproducibly achieve sensor critical dimensions (CD) less than 50 nm in magnetic recording devices while maintaining high magnetoresistive ratio and magnetic properties, limiting advancements in recording density.
Innovation Solution
A multi-step ion beam etch (IBE) process with specific energy and angle conditions is employed to trim the sidewalls of magnetoresistive sensors, involving three steps: a low incident angle for initial trimming, a high incident angle with sweeping motion for residue removal, and a low incident angle for final refinement, maintaining magnetic properties and achieving CD reduction to less than 50 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods (RIE or single-step IBE) are used to reduce sensor CD, then manufacturing simplicity is maintained, but manufacturing precision deteriorates (cannot achieve CD < 50 nm)
Solution Approach 1:
The etching process is divided into three distinct steps with different ion beam incident angles: first step at 0-15 degrees for initial trimming, second step at 45-75 degrees for residue removal, and third step at 0-15 degrees for final refinement. This segmentation allows each step to optimize for its specific function, achieving CD < 50 nm precision that cannot be obtained with conventional single-step etching.
Solution Approach 2:
The ion beam incident angle is dynamically changed between steps rather than remaining fixed. The process transitions from low angle (0-15°) to high angle (45-75°) and back to low angle (0-15°), allowing the etching characteristics to adapt to different process requirements at different stages, thereby achieving both high precision and effective residue removal.
2Manufacturing precision
If ion beam etching is used to trim sidewalls and reduce CD, then manufacturing precision improves, but magnetic properties deteriorate
Solution Approach 1:
Different regions of the sensor structure receive different ion beam treatment through controlled incident angles. The low angle steps (0-15°) provide gentle trimming that preserves magnetic properties, while the high angle step (45-75°) focuses on removing redeposited material from sidewalls. This localized quality control ensures CD precision is achieved without widespread damage to magnetic layers.
Solution Approach 2:
The high incident angle step (45-75°) is used strategically to quickly remove redeposited material that would otherwise require prolonged low-angle etching. By rushing through the residue removal phase with high-angle beams, the process minimizes total exposure time to ion beam damage while still achieving the necessary cleaning, thus preserving magnetic properties.
3Manufacturing precision
If multiple IBE steps are used to achieve CD < 50 nm, then manufacturing precision improves, but productivity deteriorates
Solution Approach 1:
The three IBE steps are performed sequentially without breaking the vacuum chamber, maintaining continuous useful action. The process transitions smoothly between different incident angles while the sensor remains in the etching chamber, eliminating the need for intermediate chamber breaks or sample reloading, thus minimizing non-productive time despite the multi-step nature of the process.
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
The process effectively reduces the free layer width to around 30 nm, enhancing recording density without degrading magnetic properties, and can be integrated into existing manufacturing lines without new tools or materials.
Implementation Method 1
A multi-step ion beam etch (IBE) process with specific energy and angle conditions is employed to trim the sidewalls of magnetoresistive sensors
Implementation Method 2
A MTJ element may be based on a TMR effect wherein a stack of layers has a configuration in which two ferromagnetic layers are separated by a thin non-magnetic dielectric layer
Implementation Method 3
The AFM layer holds the magnetic moment of the pinned layer in a fixed direction
Data Source
AI summary
A three step ion beam etch (IBE) sequence involving low energy (<300 eV) is disclosed for trimming a sensor critical dimension (free layer width=FLW) to less than 50 nm. A first IBE step has a steep incident angle with respect to the sensor sidewall and accounts for 60% to 90% of the FLW reduction. The second IBE step has a shallow incident angle and a sweeping motion to remove residue from the first IBE step and further trim the sidewall. The third IBE step has a steep incident angle to remove damaged sidewall portions from the second step and accounts for 10% to 40% of the FLW reduction. As a result, FLW approaching 30 nm is realized while maintaining high MR ratio of over 60% and low RA of 1.2 ohm-μm2. Sidewall angle is manipulated by changing one or more ion beam incident angles.