MTJ Bottom Electrode Using Diamond-Like Carbon for Etch Resistance

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Solution Overview

Problem

In magnetic tunnel junction (MTJ) devices, the bottom electrode's critical dimension (CD) often exceeds that of the MTJ pillar, leading to electrical shorts due to resputtered conductive metal particles depositing on the tunnel barrier during ion beam etching, especially when the CD is small and circularity is difficult to maintain.

Innovation Solution

A magnetic tunnel junction (MTJ) device is formed with a bottom electrode having a small critical dimension, where a diamond-like carbon (DLC) layer is used laterally adjacent to the MTJ pillar, replacing the traditional silicon nitride and organic planarization layer stack, providing higher etch resistance and reducing processing steps, and allowing for a more robust solution to punch-through issues.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the bottom electrode critical dimension is reduced to match the MTJ pillar dimension, then electrical shorts are reduced, but manufacturing precision becomes more difficult to maintain

Engineering Contradiction:

Improveelectrical short reductionVSAvoidcircularity maintenance

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

A mandrel structure is introduced as an intermediary element during the bottom electrode formation process. The mandrel serves as a template that defines the critical dimension of the bottom electrode, allowing precise control of the electrode width while maintaining circularity. The mandrel is temporarily present during fabrication and is removed afterward, having served its purpose of ensuring manufacturing precision without compromising reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If conventional materials (silicon nitride and organic planarization layer) are used, then processing steps are simpler, but etch resistance during ion beam etching is insufficient

Engineering Contradiction:

Improveprocessing stepsVSAvoidetch resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent employs a composite material structure consisting of silicon nitride combined with an organic planarization layer. This composite provides both the structural integrity and etch resistance required during ion beam etching processes. The silicon nitride layer offers high etch resistance to protect the bottom electrode, while the organic planarization layer provides surface planarity, together solving both protection and manufacturing requirements.

Inventive Principle:

Principle #40Composite materials

3Manufacturing precision

If the bottom electrode CD exceeds the MTJ pillar CD, then manufacturing is easier, but resputtered metal particles deposit on the tunnel barrier causing electrical shorts

Engineering Contradiction:

ImproveCD controlVSAvoidresputtered particle deposition

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The harmful resputtered metal particles are effectively removed or prevented from reaching the tunnel barrier. This is achieved through the use of a mandrel-defined bottom electrode geometry that minimizes particle generation, combined with process optimizations that extract or redirect particles away from the sensitive MTJ pillar region, thereby eliminating the harmful deposition effect.

Inventive Principle:

Principle #2Taking out (Extraction)

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

The use of DLC reduces the occurrence of electrical shorts and enhances the robustness of the device by maintaining the integrity of the bottom electrode's small CD, thereby improving the reliability and performance of the MTJ device.

Implementation Method 1

DLC provides a higher etch resistance to IBE than silicon nitride

Methodology Applied

Scientific EffectEtch resistance:

Implementation Method 2

ion beam etching (IBE) process is used to clean the sidewall of the MTJ pillar

Methodology Applied

Scientific EffectIon beam etching: Ion Beam

Implementation Method 3

the bottom electrode that is connected to the MTJ pillar can be a source of resputtered conductive metal particles

Methodology Applied

Scientific EffectResputtering: Sputtering

Data Source

PatentUS20200243750A1MTJ containing device containing a bottom electrode embedded in diamond-like carbon

Publication Date: 2020.07.30 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A magnetic tunnel junction (MTJ) containing device is provided in which a bottom electrode having a small CD is formed and is located laterally adjacent to diamond like carbon (DLC). DLC replaces a material stack of, from bottom to top, a silicon nitride layer and an organic planarization layer (OPL) which is typically used in providing a conductive structure having a reduced CD. DLC provides a higher etch resistance to IBE than silicon nitride, but DLC can be patterned using conventional etchants. The use of DLC thus reduces the number of processing steps for providing a reduced CD bottom electrode, and also provides a more robust solution to the issue of punch through to an underlying conductive material layer.