Replacement Bottom Electrode Structure for Misalignment Tolerant MRAM

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Solution Overview

Problem

The challenge in manufacturing magnetoresistive random access memory (MRAM) is partial yield loss due to resputtering of metal particles from the bottom electrode structure onto the sidewall of the tunnel barrier layer during ion beam etching, which is exacerbated by misalignment issues, making it difficult to scale the critical dimension of the MTJ pillar for improved switching efficiency.

Innovation Solution

A replacement bottom electrode structure process is introduced, where a sacrificial dielectric material plug is embedded in a dielectric capping layer, allowing for the formation of a MTJ pillar and top electrode structure, followed by passivation and subsequent removal of the plug to expose the conductive structure for the formation of a new bottom electrode, thereby tolerating misalignment and eliminating yield loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the MTJ pillar critical dimension is scaled down to improve switching efficiency, then switching current is reduced, but misalignment of the MTJ pillar to the bottom electrode structure occurs during ion beam etching, causing resputtering of metal particles and yield loss

Engineering Contradiction:

Improveswitching currentVSAvoidalignment precision

Core Design Contradiction:

PowerVSManufacturing precision

Solution Approach 1:

The bottom electrode structure is formed in advance before the MTJ pillar patterning process. This preliminary formation allows the bottom electrode to be ready and stable during subsequent ion beam etching, preventing resputtering issues that occur when the bottom electrode is formed after misalignment has already occurred during MTJ pillar fabrication.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces a protective layer or process intermediary that prevents direct interaction between the ion beam etching process and the bottom electrode structure. This intermediary protects the bottom electrode from resputtering during MTJ pillar formation while allowing the etching to proceed, thus eliminating yield loss from metal particle contamination.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the MTJ pillar critical dimension is increased to avoid misalignment issues, then manufacturing yield is improved, but switching efficiency and switching current deteriorate

Engineering Contradiction:

Improvemanufacturing yieldVSAvoidswitching current

Core Design Contradiction:

ProductivityVSPower

Solution Approach 1:

By forming the bottom electrode structure beforehand with precise dimensions, the patent enables subsequent MTJ pillar formation to proceed with standard critical dimensions without worrying about bottom electrode exposure. The preliminary bottom electrode structure serves as a stable foundation that tolerates normal alignment variations during ion beam etching.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent creates a protective configuration where the bottom electrode structure is formed with sufficient dimensions and positioning in advance to cushion against potential misalignment during MTJ pillar fabrication. This beforehand cushioning ensures that even with normal manufacturing variations, the bottom electrode remains protected from exposure and resputtering.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Manufacturing precision

If ion beam etching is used to pattern the MTJ material stack, then patterning precision is achieved, but resputtering of metal particles from the bottom electrode structure onto the tunnel barrier layer sidewall occurs, causing yield loss

Engineering Contradiction:

Improvepatterning precisionVSAvoidresputtering of metal particles

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The bottom electrode structure is formed and protected in advance before the ion beam etching process begins. This preliminary protective configuration counteracts the potential harmful effect of resputtering by ensuring the bottom electrode is either shielded or positioned such that ion beam exposure does not cause metal particle resputtering onto the tunnel barrier layer.

Inventive Principle:

Principle #9Preliminary anti-action

Data Source

PatentUS11165017B2Replacement bottom electrode structure process to form misalignment tolerate MRAM with high yield

Publication Date: 2021.11.02 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A replacement bottom electrode structure process is provided in which a patterned stack containing a MTJ pillar and a top electrode structure is fabricated and passivated on a sacrificial dielectric material plug that is embedded in a dielectric capping layer. The sacrificial dielectric material plug is then removed and replaced with a bottom electrode structure. The replacement bottom electrode structure process of the present application allows the MTJ patterning to be misalignment tolerate and fully eliminates the potential yield loss from the bottom electrode structure.