MTJ Electrode Formation via TaN Lateral Etching

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Solution Overview

Problem

The integration of magnetic tunnel junctions (MTJs) in back end of line (BEOL) interconnects for magnetic random access memory (MRAM) faces challenges in forming reliable electrodes and protecting landing pads during the fabrication process, which affects the performance and reliability of MRAM devices.

Innovation Solution

A method involving the deposition of a tantalum nitride (TaN) layer over MRAM regions, forming MTJ stacks, patterning and encapsulating them, and using spacers to laterally etch the TaN layer and form electrodes under the MTJ stacks, while protecting the landing pads with offset spacers and a wet etch process to prevent re-deposition and shorting.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional electrode formation methods are used in BEOL interconnects, then the fabrication process is simpler, but metallic residues reach the MTJ pillar causing reliability issues

Engineering Contradiction:

ImproveMTJ formation reliabilityVSAvoidfabrication process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The TaN barrier layer is deposited in advance over the MRAM regions before MTJ stack formation. This preliminary deposition creates a protective foundation that prevents metallic residues from reaching the MTJ pillar during subsequent fabrication steps, thereby ensuring reliability without adding complex process steps

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The TaN barrier layer serves as an intermediary protective layer between the landing pad and the MTJ pillar. It acts as a mediator that prevents direct contact between metallic residues and the MTJ structure, eliminating reliability issues while maintaining process simplicity

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If landing pads are not protected during fabrication, then the process is faster, but metallic residues cause shorting and reduce yield

Engineering Contradiction:

Improvefabrication speedVSAvoidmetallic residues causing shorting

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The TaN barrier layer is deposited beforehand to establish protective coverage over the landing pads. This preliminary action prevents metallic residues from causing shorting during the fabrication process, eliminating the need for additional protective steps and maintaining high fabrication speed

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The wet etch process, which could potentially cause damage, is converted into a beneficial cleaning mechanism. By using wet etch to remove the TaN layer after electrode formation, metallic residues are prevented from reaching the MTJ pillar, and the process actually improves yield by eliminating shorting risks

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If multiple planarization and masking steps are used to protect MTJ, then reliability improves, but manufacturing complexity and time increase

Engineering Contradiction:

ImproveMTJ protection reliabilityVSAvoidfabrication time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The protective function and the electrode formation function are merged into a single TaN barrier layer deposition step. This eliminates the need for separate planarization and masking steps, reducing fabrication time while maintaining MTJ protection reliability

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The TaN barrier layer performs multiple functions simultaneously: it protects the landing pad during fabrication, serves as an electrode material, and prevents metallic residues from reaching the MTJ pillar. This multi-functionality eliminates the need for additional protective steps, reducing fabrication time without compromising reliability

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 reliability of MTJ formation by protecting landing pads and preventing metallic residues from reaching the MTJ pillar, reducing planarization and masking steps, and ensuring the formation of a bottom electrode that does not leave residues, thus improving the yield and performance of MRAM devices.

Implementation Method 1

a wet etch process to prevent re-deposition and shorting

Methodology Applied

Scientific EffectWet etch:

Implementation Method 2

depositing a barrier layer, such as a tantalum nitride (TaN) layer, over a dielectric incorporating magnetic random access memory (MRAM) regions

Methodology Applied

Scientific EffectDeposition: Deposition (physical)

Data Source

PatentUS10319783B2Integrated magnetic tunnel junction (MTJ) in back end of line (BEOL) interconnects

Publication Date: 2019.06.11 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A method is presented for forming a semiconductor structure. The method includes depositing a barrier layer, such as a tantalum nitride (TaN) layer, over a dielectric incorporating magnetic random access memory (MRAM) regions, forming magnetic tunnel junction (MTJ) stacks over portions of the TaN layer, patterning and encapsulating the MTJ stacks, forming spacers adjacent the MTJ stacks, and laterally etching sections of the TaN layer, after spacer formation, to form an electrode under the MTJ stacks. The electrode protects the MRAM regions. The electrode can be recessed from the spacers.