Conductive Hard Mask for MTJ Etch Damage
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Solution Overview
Problem
Magnetic tunnel junction (MTJ) devices are susceptible to process-related damages during etching, such as re-deposition of etching byproducts, which can lead to reduced magnetic resistance ratios and lower yields in high-density arrays, as existing techniques fail to effectively protect the MTJ stack from these damages.
Innovation Solution
A multi-step etching process is implemented, where a spacer is protected during the second etching step, involving conformal deposition of a first spacer layer, selective removal to create a recess, and filling with a conductive material to form a second conductive hard mask, which aligns with the first spacer and protects the MTJ stack from re-deposition and plasma damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional single-step etching process is used, then the manufacturing process is simple and fast, but the MTJ stack is susceptible to re-deposition of etching byproducts and plasma damage, reducing magnetic resistance ratio and yield
Solution Approach 1:
The etching process is divided into multiple steps with different etching chemistries and parameters. The first etching step uses a protective spacer mask to etch only the non-magnetic layers, while the second etching step removes the spacer and completes the etching of magnetic layers. This segmentation allows each step to be optimized for its specific function, protecting the MTJ stack from damage while maintaining process efficiency.
Solution Approach 2:
A spacer layer is deposited conformally on the MTJ stack before the etching process begins. This spacer serves as a protective mask during the first etching step, preventing re-deposition of etching byproducts on the magnetic layers. The preliminary placement of this protective layer ensures the magnetic stack is shielded before exposure to the etching plasma.
2Reliability
If existing protection techniques are applied, then some damage is reduced, but they fail to effectively protect against re-deposition and plasma damage in high-density arrays
Solution Approach 1:
The spacer layer acts as an intermediary protective element between the etching plasma and the MTJ stack. It physically intercepts re-deposited etching byproducts and plasma species, preventing them from reaching and damaging the magnetic layers. This intermediary layer can be selectively removed after serving its protective function, leaving the MTJ stack intact.
Solution Approach 2:
The protective spacer mask is applied locally and selectively to specific regions of the wafer where MTJ stacks are located. The spacer provides enhanced protection in these critical areas while allowing other regions to be processed differently. This localized approach optimizes protection effectiveness without unnecessarily complicating the entire fabrication process.
3Manufacturing precision
If the spacer is exposed to the second etching step without protection, then the etching can be completed, but the spacer erodes and loses its protective function, allowing damage to the MTJ stack
Solution Approach 1:
The spacer mask is designed to be dynamically adjusted between etching steps. During the first etching step, the spacer is intact and provides full protection. Between steps, the spacer is selectively removed or thinned to allow the second etching chemistry to access and complete the etching of magnetic layers. This dynamic modification of the spacer enables it to serve different functions at different stages.
Solution Approach 2:
The etching process employs periodic alternation between protective and aggressive etching modes. The first periodic phase uses the spacer-protected etching to remove non-magnetic layers with minimal damage. The second periodic phase removes the spacer and completes the magnetic layer etching. This periodic switching between protection and exposure allows precise control over when the spacer provides protection and when it is removed to enable complete etching.
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 reduces process-related damages, enhancing the magnetic resistance ratio and yield in high-density MTJ arrays by physically separating re-deposition materials and plasma from the active magnetic layers, thereby maintaining the integrity of the MTJ stack.
Implementation Method 1
conformally depositing a first spacer layer on a first conductive hard mask, on a first electrode layer, and on magnetic layers of the MTJ
Implementation Method 2
filling the recess with a conductive material to form a second conductive hard mask
Data Source
AI summary
A multi-step etch technique for fabricating a magnetic tunnel junction (MTJ) apparatus includes forming a first conductive hard mask on a first electrode of the MTJ apparatus for etching the first electrode during a first etching step. The method also includes forming a second conductive hard mask on the first conductive hard mask for etching magnetic layers of the MTJ apparatus during a second etching step. A spacer layer is conformally deposited on sidewalls of the first conductive hard mask. The second conductive hard mask is deposited on the first conductive hard mask and aligned with the spacer layer on the sidewalls of the first conductive hard mask.