Beveled MTJ Pillar Structure for Void-Free ILD Fill
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Solution Overview
Problem
In high-performance magneto-resistive random access memory (MRAM) devices, voids in the interlevel dielectric (ILD) between magnetic tunnel junction (MTJ) pillars can lead to electric shorts during top contact material deposition, necessitating improved designs to prevent void formation.
Innovation Solution
The implementation of beveled device layers with a specific width gradient and encapsulation layers for the MTJ pillars, ensuring low aspect ratio structures that reduce void formation during ILD deposition, thereby preventing top contact shorts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If blanket MTJ stacks are patterned to form embedded MTJ pillar structures, then device integration is achieved, but voids form in the ILD between top electrodes and top contact metals
Solution Approach 1:
The patent applies asymmetry by introducing a bevel angle to the MTJ pillar structure. The pillars are formed with non-vertical sidewalls at a specific bevel angle (e.g., 5-15 degrees from vertical), creating an asymmetric geometry that prevents void formation during ILD deposition. This asymmetric shape allows the ILD material to flow and fill the space completely without trapping air pockets, thereby maintaining reliability while preserving device integration benefits.
Solution Approach 2:
The patent changes the geometric parameters of the MTJ pillars by introducing a controlled bevel angle. Instead of vertical sidewalls, the pillars are formed with tapered sidewalls where the width at the top differs from the width at the bottom. This parameter change in the pillar geometry (from cylindrical to frustoconical shape) fundamentally alters the deposition dynamics, enabling complete ILD fill without voids while maintaining the embedded pillar structure for device integration.
2Ease of manufacture
If ILD is deposited to fill inter-pillar spaces, then connection to BEOL wiring is enabled, but contact material fills voids resulting in electric shorts
Solution Approach 1:
The beveled pillar geometry creates an asymmetric profile that guides the ILD and subsequent contact material deposition. The tapered sidewalls ensure that materials deposit uniformly from the walls toward the center, preventing the formation of suspended bridges or droplets that could create shorts. The asymmetric shape promotes complete filling behavior where the contact material reaches the bottom of the trench uniformly without forming conductive bridges across the pillar gap.
Solution Approach 2:
The patent performs a preliminary action by forming the beveled pillar structure before ILD and contact material deposition. This pre-formed geometric configuration acts as a template that directs subsequent material deposition, ensuring that the ILD and contact materials fill the spaces in a controlled manner. The preliminary bevelled shape prevents the formation of voids and potential short circuits before the problematic deposition steps occur.
3Device complexity
If vertical MTJ pillars are used, then simple fabrication is maintained, but voids form during ILD deposition
Solution Approach 1:
The patent introduces a moderate level of geometric complexity by applying a bevel angle to the MTJ pillars. This asymmetric modification is achieved through standard semiconductor fabrication techniques such as angled etching or oblique deposition, which are routine industrial processes. The added geometric complexity is minimal and does not significantly increase fabrication steps, while it completely eliminates the void formation problem associated with vertical pillars.
Solution Approach 2:
The patent modifies a single key parameter of the pillar geometry - the sidewall angle - while maintaining the overall vertical orientation and embedded structure. This parameter change from 90 degrees (vertical) to a slightly tapered angle (e.g., 85-95 degrees from horizontal) is sufficient to prevent void formation. The modification is achieved through controlled deposition or etching conditions, adding minimal complexity to the fabrication process while solving the void formation issue.
Data Source
AI summary
A memory device includes a magnetic tunnel junction pillar located between, and electrically connected to, a bottom electrode and a top electrode. The magnetic tunnel junction pillar is composed of a plurality of device layers vertically stacked above the bottom electrode. Each of the plurality of device layers, the top electrode, and the bottom electrode is formed at a first bevel angle. A bottommost portion of each of the plurality of device layers in the magnetic tunnel junction pillar has a width that is greater than a width of a topmost portion of each preceding device layer. An encapsulation layer is disposed along opposite sidewalls of the top electrode, opposite sidewalls of the bottom electrode, and opposite sidewalls of each of the plurality of device layers.