Thin Metallic Hard Mask for High-Density MRAM IBE Sidewall Cleaning
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Solution Overview
Problem
Conventional methods for etching magnetic tunnel junctions (MTJ) in high-density MRAM arrays face challenges with chemical reactions damaging the magnetic properties and limited ion beam etching (IBE) angles due to small feature sizes and increased cell density, leading to re-deposited material and shorting failures.
Innovation Solution
A thin metallic hard mask, preferably a bi-layer film with ruthenium and tantalum layers, is used to increase the IBE incident angle for sidewall cleaning without compromising the process margin for subsequent interconnection, allowing for effective removal of re-deposited and damaged materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thick hard mask is used to gain process margin for subsequent interconnection, then the process margin is improved, but the IBE incident beam angle is limited and re-deposited material cannot be effectively removed
Solution Approach 1:
The patent segments the hard mask into multiple layers with different functions: a thin top hard mask layer (10-40 nm) that allows high IBE angles for sidewall cleaning, and a thicker bottom hard mask layer that provides the necessary process margin for interconnection. This segmentation resolves the contradiction by assigning different thickness requirements to different functional layers.
Solution Approach 2:
The patent transitions from a single-layer hard mask to a multi-layer hard mask structure, adding the dimensional aspect of layering. This allows the system to simultaneously satisfy both the thinness requirement for IBE access and the thickness requirement for process margin in the vertical dimension.
2Productivity
If the MTJ feature size is decreased to increase cell density, then the cell density is improved, but the ratio of damaged MTJ increases and magnetic properties are degraded
Solution Approach 1:
The patent applies preliminary cleaning action using high-angle IBE before subsequent processing steps. By removing re-deposited and damaged material from MTJ sidewalls before interconnection formation, the method prevents magnetic property degradation even as cell density increases and feature sizes shrink.
Solution Approach 2:
The patent changes the IBE incident beam angle parameter to high angles (greater than 45 degrees) specifically for sidewall cleaning operations. This parameter change enables effective removal of damaged material from small-featured MTJ structures, maintaining magnetic properties despite increased cell density.
3Object-generated harmful factors
If a high incident beam angle is used to remove re-deposited material from sidewalls, then the sidewall cleaning is improved, but the pitch between adjacent MTJ pillars must be increased which reduces cell density
Solution Approach 1:
The patent segments the etching process into distinct stages: a first IBE process with high incident angles for sidewall cleaning, and subsequent processes for interconnection formation. This segmentation allows high-angle IBE to be applied without requiring increased pitch, as the cleaning occurs in-place before other structures are added.
Solution Approach 2:
The patent performs sidewall cleaning as a preliminary action before forming interconnection structures. By cleaning the sidewalls first with high-angle IBE, the method eliminates the need to increase pitch for cleaning access, as the cleaning occurs before surrounding structures are added.
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 increased IBE angle enhances the removal of re-deposited and damaged materials from MTJ sidewalls, improving yield and reducing magnetic property variations across the wafer, while maintaining sufficient thickness for interconnection processes.
Implementation Method 1
The ion beam etching (IBE) process which is well established in the magnetic head industry could be another option for the MTJ etching because the IBE process is known to be free of chemical reactions
Implementation Method 2
the IBE process is known to be free of chemical reactions
Data Source
AI summary
Embodiments of the invention are described that use a thin metallic hard mask, which can be a bi-layer film, to increase the incident IBE angle for MTJ sidewall cleaning without losing the process margin for the subsequent interconnection process. The patterned metallic hard mask pads also serve as the top electrode for the MTJ cells. Using a thin metallic hard mask is possible when the hard mask material acts as a CMP stopper without substantial loss of thickness. In the first embodiment, the single layer hard mask is preferably ruthenium. In the second embodiment, the lower layer of the bi-layer hard mask is preferably ruthenium. The wafer is preferably rotated during the IBE process for uniform etching. A capping layer under the hard mask is preferably used as the etch stopper during hard mask etch process in order not to damage or etch through the upper magnetic layer.