Self-Aligned Double Patterning for Dense MTJ Arrays
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Solution Overview
Problem
Conventional methods for manufacturing non-volatile magnetic random access memory (MRAM) face limitations in achieving dense arrays of magnetic tunnel junctions (MTJs) due to critical dimension control issues in photolithography, leading to increased program current and topography challenges.
Innovation Solution
The implementation of a self-aligned double patterning method using orthogonal line patterning steps and a thin dielectric mask to reduce the size of MTJs, allowing for half-pitch capability and aspect ratios greater than one, while minimizing program current without layout changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithography is used for patterning MTJ elements, then the process is simple and straightforward, but the critical dimension control is poor leading to larger MTJ size
Solution Approach 1:
The patent divides the patterning process into two separate photolithography steps: first forming mandrels with initial pitch, then forming spacers around mandrels to achieve half-pitch features. This segmentation allows each step to work within conventional lithography limits while achieving superior final resolution.
Solution Approach 2:
The patent performs preliminary patterning of mandrels before forming the final MTJ structures. The mandrels serve as preliminary features that guide subsequent spacer formation, enabling precise positioning of final patterns without requiring direct patterning at the target pitch.
2Productivity
If MTJ size is reduced to increase array density, then packing efficiency improves, but program current increases
Solution Approach 1:
The patent changes the aspect ratio of MTJ elements from square (1:1) to rectangular with aspect ratio greater than 1. This dimensional change allows one dimension to be reduced for higher density while the other dimension compensates to maintain adequate barrier area and limit program current increase.
3Reliability
If thick dielectric mask is used for patterning, then etch protection is sufficient, but topography and gap filling become problematic
Solution Approach 1:
The patent uses a thin dielectric mask layer instead of a thick mask. The thin film provides sufficient etch protection for the patterning process while minimizing topography buildup, eliminating the need for complex gap filling operations that would be required with thick masks.
Data Source
AI summary
Methods of fabricating MTJ arrays using two orthogonal line patterning steps are described. Embodiments are described that use a self-aligned double patterning method for one or both orthogonal line patterning steps to achieve dense arrays of MTJs with feature dimensions one half of the minimum photo lithography feature size (F). In one set of embodiments, the materials and thicknesses of the stack of layers that provide the masking function are selected so that after the initial set of mask pads have been patterned, a sequence of etching steps progressively transfers the mask pad shape through the multiple mask layer and down through all of the MTJ cell layers to the form the complete MTJ pillars. In another set of embodiments, the MTJ/BE stack is patterned into parallel lines before the top electrode layer is deposited.