SOT-MRAM Integration via One-Step Etch for Reliable Contact
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current integration schemes for three terminal SOT switching devices face challenges in reliably patterning thin heavy metal layers, leading to structural integrity issues and increased complexity, as the etch process often results in overetching of the FM layer, causing contact loss with the underlying bottom electrode and rendering the device unusable.
Innovation Solution
A one-step etch process is employed to form coplanar sidewalls on both the FM and SHE layers, using ion beam etching to stop on the top surface of the bottom electrodes, ensuring the SHE layer remains intact and forms a conductive bridge between adjacent electrodes, thereby reducing the number of process steps and improving reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional multi-step etch process is used to pattern the heavy metal layer and FM layer separately, then the patterning precision may be improved, but the process complexity increases and overetching of the FM layer occurs causing contact loss
Solution Approach 1:
The patent combines the etching of the heavy metal layer and FM layer into a single etch process step. The etch process is configured to etch both layers simultaneously to the same depth, forming coplanar sidewalls without requiring separate etch steps. This merging of operations reduces process complexity while maintaining patterning precision through proper etch parameter control and layer thickness design.
Solution Approach 2:
The single etch process serves multiple functions: it patterns both the heavy metal layer and FM layer, forms coplanar sidewalls for both layers, and creates the conductive bridge structure. This multi-functional approach eliminates the need for separate patterning steps and reduces overall process complexity while achieving the required manufacturing precision.
2Manufacturing precision
If the etch process is extended to ensure complete removal of FM layer material, then the patterning completeness is improved, but the heavy metal layer is overetched causing contact loss with bottom electrode
Solution Approach 1:
The patent carefully controls etch parameters including etch depth, etch rate, and process timing to achieve the precise stopping point at the bottom electrode interface. By optimizing these parameters, the etch process completes the removal of FM layer material while preventing overetching of the heavy metal layer, thus maintaining both patterning completeness and contact integrity.
Solution Approach 2:
The heavy metal layer is designed with sufficient thickness beforehand to serve as an etch stop layer. This preliminary design ensures that when the etch process reaches the bottom electrode, the heavy metal layer remains intact and maintains electrical contact, preventing the overetching problem while allowing complete FM layer removal.
3Manufacturing precision
If multiple separate etch steps are used to pattern different layers, then the manufacturing precision is improved, but the number of process steps increases leading to higher fabrication costs
Solution Approach 1:
The patent merges the patterning of the heavy metal layer and FM layer into a single etch operation. This consolidation reduces the total number of process steps, simplifies manufacturing, and lowers fabrication costs while maintaining patterning accuracy through controlled etch parameters and proper layer design.
Solution Approach 2:
The single etch process performs multiple patterning functions simultaneously, creating patterns in both the heavy metal and FM layers while forming coplanar sidewalls. This multi-functional approach eliminates redundant process steps and reduces overall manufacturing complexity and cost.
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 enhances the structural integrity and reliability of the SOT-MRAM devices by maintaining contact between the heavy metal and FM layers, reducing process complexity, and lowering fabrication costs while ensuring independent reading and writing paths.
Implementation Method 1
a thin heavy metal layer generates a Spin Hall Effect involving spin orbit torque on an adjoining ferromagnetic (FM) layer thereby switching the FM magnetization
Implementation Method 2
using ion beam etching to stop on the top surface of the bottom electrodes
Data Source
AI summary
A three terminal spin-orbit-torque (SOT) device is disclosed wherein a free layer (FL) with a switchable magnetization is formed on a Spin Hall Effect (SHE) layer comprising a Spin Hall Angle (SHA) material. The SHE layer has a first side contacting a first bottom electrode (BE) and an opposite side contacting a second BE where the first and second BE are separated by a dielectric spacer. A first current is applied between the two BE, and the SHE layer generates SOT on the FL thereby switching the FL magnetization to an opposite perpendicular-to-plane direction. The SHE layer is a positive or negative SHA material, and may be a topological insulator such as Bi2Sb3. A top electrode is formed on an uppermost hard mask in each SOT device. A single etch through the FL and SHE layer ensures a reliable first current pathway that is separate from a read current pathway.