MTJ Etching via Segmented Photo-Resist Masks
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Solution Overview
Problem
The manufacturing of magnetic random access memory (MRAM) elements faces challenges in fabricating scalable and reliable magnetic tunnel junctions (MTJs) due to metal redeposition onto the barrier layer during etching, causing shorting between the fixed and free layers.
Innovation Solution
A method involving a series of etching processes using photo-resists as masks to control the width and length of the MTJ layers, stopping etching when a predetermined material is detected to prevent metal deposition on the barrier layer, ensuring reliable connection and avoiding shorting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single etching process is used to form the magnetic memory element, then the manufacturing process is simpler and faster, but metal layers below the MgO barrier layer are re-deposited onto the MgO layer causing shorting between fixed and free layers
Solution Approach 1:
The single etching process is divided into multiple sequential etching steps with different photo-resist masks. The first etching step uses a first photo-resist to etch the oxide layer, and the second etching step uses a second photo-resist to etch the metal layers. This segmentation prevents metal redeposition onto the MgO barrier layer while maintaining manufacturing efficiency.
Solution Approach 2:
The oxide layer is etched in advance using the first photo-resist before the metal layers are etched. This preliminary action removes the oxide protective layer that would otherwise prevent proper etching of the metal layers, and establishes the structural foundation for the subsequent metal layer etching step.
2Ease of manufacture
If the oxide layer is completely removed during etching, then better access to metal layers is achieved, but metal redeposition onto the MgO layer occurs causing shorting
Solution Approach 1:
The etching process is segmented into two distinct steps: first etching the oxide layer with a first photo-resist, then etching the metal layers with a second photo-resist. This segmentation allows controlled access to metal layers without causing harmful metal redeposition onto the MgO barrier layer.
Solution Approach 2:
The first photo-resist acts as an intermediary that enables selective removal of the oxide layer without directly exposing the metal layers to conditions that would cause harmful redeposition. The second photo-resist then serves as another intermediary for the controlled etching of metal layers.
3Manufacturing precision
If photo-resist is used as mask during etching, then precise control of MTJ layer width and length is achieved, but additional manufacturing steps are required
Solution Approach 1:
The manufacturing process is segmented into multiple etching steps, each with its own photo-resist mask application. This segmentation enables precise dimensional control of MTJ layers by allowing independent optimization of each etching step's parameters and mask patterns.
Solution Approach 2:
Photo-resist is applied and removed in multiple partial cycles rather than a single continuous process. Each photo-resist application targets specific layers and dimensions, allowing precise control while managing the overall complexity through focused, partial actions rather than comprehensive simultaneous processing.
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 effectively prevents shorting between the fixed and free layers, allowing for a reliable and scalable manufacturing process of MRAM elements with improved connection to external circuitry, maintaining the magnetic orientation of the fixed layer and switchable characteristics of the free layer.
Implementation Method 1
using the hard mask to perform a series of etching processes to reduce the width of the MTJ and the top electrode to substantially a desired width
Implementation Method 2
A method involving a series of etching processes using photo-resists as masks to control the width and length of the MTJ layers
Implementation Method 3
a barrier or MgO layer, formed below the free layer... the barrier layer is obviously not a metal layer whereas the free and fixed layers are made of metal
Data Source
AI summary
A method of manufacturing a magnetic memory element includes the steps of forming a permanent magnetic layer on top a bottom electrode, forming a pinning layer on top the permanent magnetic layer, forming a magnetic tunnel junction (MTJ) including a barrier layer on top of the pinning layer, forming a top electrode on top of the MTJ, forming a hard mask on top of the top electrode, and using the hard mask to perform a series of etching processes to reduce the width of the MTJ and the top electrode to substantially a desired width, where one of these etching processes is stopped when a predetermined material in the pinning layer is detected thereby avoiding deposition of metal onto the barrier layer of the etching process thereby preventing shorting.