Self-Aligned MTJ Fabrication Without Lithography Masks
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Solution Overview
Problem
The existing methods for fabricating spin-transfer torque magnetic random-access memory (STT-MRAM) require costly and time-consuming use of multiple lithography masks, making the process inefficient for forming magnetic tunnel junctions (MTJs).
Innovation Solution
A self-aligned MTJ is formed without using lithography masks by recessing a metal layer in a low-k dielectric layer, depositing electrodes and MTJ layers with minimal sidewall coverage, and planarizing silicon nitride-based layers to achieve a self-aligned structure, allowing for high-density MTJ formation using dual-damascene patterning and minimal additional masks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lithography masks are used to form MTJ structures, then manufacturing precision can be achieved, but fabrication cost and processing time increase significantly
Solution Approach 1:
The patent implements self-aligned fabrication where the MTJ structure automatically aligns itself during the formation process. The bottom electrode pattern serves as the alignment reference for subsequent layers, eliminating the need for external lithography masks. This self-service mechanism maintains manufacturing precision while dramatically improving fabrication throughput by removing mask-related process steps.
Solution Approach 2:
The patent performs preliminary patterning of the bottom electrode layer before forming subsequent MTJ layers. This preliminary action establishes the alignment reference early in the process, allowing subsequent layers to be deposited and patterned without requiring additional lithography masks, thus resolving the contradiction between precision and productivity.
2Manufacturing precision
If multiple lithography masks are used for MTJ fabrication, then structural alignment is achieved, but fabrication complexity and cost increase
Solution Approach 1:
The patent merges the alignment function into the structural formation process itself. By using the bottom electrode pattern as the inherent alignment reference and depositing subsequent layers (tunnel barrier, top electrode) in a self-aligned manner, the patent combines multiple alignment functions into a single integrated process, reducing both fabrication complexity and cost while maintaining layer alignment precision.
Solution Approach 2:
The patent extracts the lithography mask step from the fabrication process entirely. By implementing self-aligned deposition and patterning techniques, the patent removes the external alignment tool (lithography mask) while maintaining alignment precision through the inherent geometric relationships established during structure formation.
3Reliability
If conventional MTJ fabrication methods are used, then device functionality is achieved, but production efficiency decreases due to multiple masking steps
Solution Approach 1:
The patent implements continuous deposition and patterning processes for forming the MTJ stack. By using self-aligned techniques where each layer is formed continuously on the previously formed layer without interruption for mask application and removal, the patent maintains device functionality while minimizing wafer processing time and eliminating idle time associated with mask-based fabrication.
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 eliminates the need for lithography masks, reducing fabrication costs and time while enabling the formation of high-density self-aligned MTJs, suitable for advanced semiconductor devices like those in the 28 nm technology node and beyond.
Implementation Method 1
recessing the metal layer in the low-k dielectric layer by wet etching
Implementation Method 2
forming the first and second electrodes and the MTJ layer by directional deposition with minimal sidewall coverage
Implementation Method 3
planarizing the silicon nitride-based layer down to the second electrode
Data Source
AI summary
A method of forming a self-aligned MTJ without using a photolithography mask and the resulting device are provided. Embodiments include forming a first electrode over a metal layer, the metal layer recessed in a low-k dielectric layer; forming a MTJ layer over the first electrode; forming a second electrode over the MTJ layer; removing portions of the second electrode, the MTJ layer, and the first electrode down to the low-k dielectric layer; forming a silicon nitride-based layer over the second electrode and the low-k dielectric layer; and planarizing the silicon nitride-based layer down to the second electrode.