Ion Beam Etch for Magnetic Tunnel Junction Free Layer Width
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for fabricating magnetoresistive sensors, such as magnetic tunnel junctions, are unable to reliably achieve a free layer width of 20-25 nm while maintaining high magnetoresistive ratio and other magnetic properties, which is necessary for advanced magnetic recording devices.
Innovation Solution
A two-part ion beam etch sequence is employed, involving a low incident angle etch process followed by a high incident angle sweeping motion etch process, to reduce the free layer width to 20-25 nm while maintaining the magnetic properties, using a MTJ stack configuration with a non-magnetic spacer between ferromagnetic layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithography and reactive ion etch methods are used to reduce sensor critical dimension, then the manufacturing process is simple and easy to implement, but the critical dimension cannot be reduced below 30 nm reliably
Solution Approach 1:
The etch process is divided into multiple sequential steps with different incident angles. The first step uses a low incident angle (0-30 degrees) to perform the bulk etching, and the second step uses a high incident angle (60-90 degrees) to perform the final precision etching. This segmentation allows each step to be optimized for its specific function, achieving both efficiency and precision.
Solution Approach 2:
The incident angle of the ion beam is dynamically changed between etching steps. By adjusting the incident angle according to the etching stage, the process adapts to different requirements: low angle for material removal efficiency and high angle for dimensional precision and sidewall control.
2Manufacturing precision
If the free layer width is reduced to increase recording density, then the recording capacity improves, but the magnetic properties and magnetoresistive ratio deteriorate
Solution Approach 1:
Different regions of the etching process are given different qualities: the first etching step targets the bulk material removal with low angle incidence, while the second step targets the critical dimension definition with high angle incidence. This local optimization ensures that each region of the process contributes maximally to the overall goal of achieving small dimensions with good magnetic properties.
Solution Approach 2:
The incident angle parameter is changed between etching steps to optimize different aspects of the etching process. The low incident angle in the first step maximizes etching rate, while the high incident angle in the second step maximizes dimensional control and minimizes damage to magnetic properties.
3Manufacturing precision
If a single high incident angle etch process is used to achieve small critical dimension, then the etching precision is high, but the etching rate is low and the process time is long
Solution Approach 1:
The etch process is segmented into two distinct steps: a first step for bulk material removal and a second step for precision dimensioning. This segmentation allows the process to achieve both high productivity (in the first step) and high precision (in the second step), avoiding the trade-off that would exist in a single-step process.
Solution Approach 2:
The etching process uses periodic action with alternating incident angles. The low incident angle phase removes material efficiently, and the high incident angle phase refines the dimension, creating a periodic cycle that combines high productivity with high precision throughout the overall 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
This method effectively reduces the free layer width by up to 30 nm compared to the photoresist mask layer, achieving dimensions required for high-performance recording devices while preserving the magnetic properties of the sensor.
Implementation Method 1
a first ion beam etch process is performed with ions having an incident angle of 0 degrees to 30 degrees with respect to a plane perpendicular to the planes of the MTJ stack of layers
Data Source
AI summary
A two part ion beam etch sequence involving low energy (<300 eV) is disclosed for fabricating a free layer width (FLW) as small as 20-25 nm in a MTJ element. A first etch process has one or more low incident angles and accounts for removal of 70% to 100% of the MTJ stack that is not covered by an overlying photoresist layer. The second etch process employs one or more high incident angles and a sweeping motion that is repeated during a plurality of cycles. Sidewall slope may be adjusted by varying the incident angle during either of the etch processes. FLW is about 30 nm less than an initial critical dimension in the photoresist layer while maintaining a MR ratio over 60% and low RA (resistance×area) value of 1.0 ohm-μm2.