MTJ Layer Stack Cr Seed Barrier
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Solution Overview
Problem
Magnetic tunnel junction (MTJ) devices face performance degradation due to elevated temperatures during back end of line (BEOL) processing, as Fe from the reference layer diffuses into other layers, causing loss of anisotropy and reduced coercivity and tunnel magneto-resistance ratio (TMR).
Innovation Solution
A layer stack for MTJ devices is formed with a seed layer structure comprising a Ru-comprising layer and a Cr-comprising layer, where Cr diffuses into the pinning layer, blocking Fe diffusion and reducing thermal-induced diffusion of Fe into the pinning layer, thereby maintaining the magnetic and electric properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Fe-comprising reference layer structure is used in MTJ device, then favorable magnetic and electric properties (high TMR) are achieved, but Fe diffuses into pinning layer during elevated temperature processing, causing loss of anisotropy and reduced coercivity
Solution Approach 1:
A Cr-comprising layer is introduced as an intermediary between the Fe-comprising reference layer and the pinning layer structure. This intermediate layer acts as a diffusion barrier that prevents Fe atoms from migrating into the pinning layer during elevated temperature processing, while still allowing the MTJ device to maintain its favorable magnetic and electric properties through the Fe-comprising reference layer.
Solution Approach 2:
The seed layer structure is segmented into multiple distinct layers: a Ru-comprising layer and a Cr-comprising layer. This segmentation allows each layer to perform its specific function - the Ru layer provides structural foundation and the Cr layer provides diffusion blocking - thereby solving the contradiction between maintaining Fe-comprising reference layer properties and preventing Fe diffusion during thermal processing.
2Ease of manufacture
If elevated temperature processing (400°C or greater) is used for BEOL interconnect structure, then interconnection structure and metal interconnects are formed, but thermal-induced diffusion of Fe into pinning layer causes performance degradation
Solution Approach 1:
The Cr-comprising layer is deposited in advance during the MTJ layer deposition process, before the elevated temperature BEOL processing occurs. This preliminary action establishes a diffusion barrier that will protect the pinning layer structure from Fe diffusion when the device subsequently undergoes thermal processing at 400°C or greater for interconnect formation.
Solution Approach 2:
The Cr-comprising layer serves as a protective intermediary that allows the BEOL processing to proceed at elevated temperatures for manufacturing purposes while preventing the harmful thermal-induced diffusion of Fe into the pinning layer, thus decoupling the manufacturing requirements from the device performance degradation.
3Reliability
If pinning layer structure is used to fix magnetization of reference layer, then perpendicular magnetic anisotropy and high TMR are achieved, but Fe diffusion into pinning layer causes loss of anisotropy and reduced coercivity
Solution Approach 1:
The Cr-comprising layer is positioned as an intermediary between the Fe-comprising reference layer and the pinning layer structure. It selectively blocks Fe diffusion into the pinning layer while allowing the pinning layer to maintain its function of fixing the magnetization of the reference layer through exchange coupling, thereby preserving both the perpendicular magnetic anisotropy and high TMR ratio.
Solution Approach 2:
The diffusion barrier property is localized to the Cr-comprising layer, which is strategically positioned only where Fe diffusion would harm the pinning layer structure. This localized application of diffusion blocking allows the rest of the MTJ structure to maintain its optimal magnetic properties without interference.
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 proposed layer stack effectively reduces Fe diffusion, preventing performance degradation of MTJ devices during elevated temperature processing, ensuring stable magnetic and electric properties.
Implementation Method 1
Cr diffuses from the Cr-comprising layer into the pinning layer structure
Data Source
AI summary
The disclosed technology relates generally to semiconductor devices, and more particularly to a layer stack for a magnetic tunnel junction (MTJ) device, and a method of forming the same. According to an aspect, a layer stack for a (MTJ) device comprises a seed layer structure, a pinning layer structure arranged above the seed layer structure, and above the pinning layer structure a Fe-comprising reference layer structure and a free layer structure separated by a tunnel barrier layer. The seed layer structure comprises a Ru-comprising layer and a Cr-comprising layer. The Cr-comprising layer forms an upper layer of the seed layer structure.