Gas Cluster Ion Etching for MTJ Perpendicular Sidewalls

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Solution Overview

Problem

Conventional dry etching methods, such as RIE, struggle to achieve a perpendicular sidewall shape in magnetic tunnel junction (MTJ) devices due to the difficulty in etching magnetic metals like cobalt and iron, leading to degraded switching properties and increased yield loss due to redeposition issues.

Innovation Solution

The use of ionized gas clusters to etch the MTJ device, allowing for precise control of the etching process and achieving a perpendicular sidewall shape by irradiating gas cluster ions perpendicularly onto the surface, thereby reducing redeposition and maintaining the integrity of the tunneling barrier layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If conventional dry etching (RIE) is used to pattern MTJ devices, then the etching process can be performed, but the sidewall angle cannot be substantially perpendicular and the width increases downward

Engineering Contradiction:

Improvesidewall angleVSAvoidwidth control

Core Design Contradiction:

ShapeVSManufacturing precision

Solution Approach 1:

The patent changes the etching parameters by using gas cluster ion beam (GCIB) etching instead of conventional RIE. This involves changing the ion source from plasma ions to gas cluster ions, changing the ion energy distribution, and modifying the etching chemistry to achieve perpendicular sidewalls and precise width control in MTJ devices

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the conventional plasma-based chemical etching mechanism with a gas cluster ion beam physical etching mechanism. This substitution allows for better control over etching profiles and reduces the formation of redeposition layers that cause width increase

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Productivity

If MTJ device is patterned using dry etching with short distance between storage layer and reference layer, then high density is achieved, but redeposition of metal may straddle the tunneling barrier layer causing short circuits

Engineering Contradiction:

Improvedevice densityVSAvoidyield

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent converts the potential harm of redeposition by using gas cluster ion beam etching that produces minimal redeposition compared to conventional RIE. The physical sputtering mechanism of GCIB removes material cleanly without the chemical redeposition that occurs in plasma etching, thereby preventing short circuits even at high device densities

Inventive Principle:

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

Solution Approach 2:

The patent introduces gas cluster ions as an intermediary etching species that mediates between the ion beam and the MTJ device structure. These gas cluster ions provide gentle yet effective etching that removes material without causing the aggressive redeposition that would bridge the thin tunneling barrier layer between storage and reference layers

Inventive Principle:

Principle #24Intermediary (Mediator)

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 method effectively patterns MTJ devices with perpendicular sidewalls, maintaining the magnetic properties and reducing defects, thus enhancing the yield and reliability of high-density MRAM fabrication.

Implementation Method 1

etching a portion of the second magnetic layer and a portion of the first magnetic layer by irradiating gas clusters onto a portion of a surface of the second magnetic layer or a portion of a surface of the first magnetic layer

Methodology Applied

Scientific EffectIon beam etching: Ion Beam

Data Source

PatentUS8981507B2Method for manufacturing nonvolatile memory device

Publication Date: 2015.03.17 KIOXIA CORP

AI summary

According to one embodiment, a method for manufacturing a nonvolatile memory device including a plurality of memory cells is disclosed. Each of the plurality of memory cells includes a base layer including a first electrode, a magnetic tunnel junction device provided on the base layer, and a second electrode provided on the magnetic tunnel junction device. The magnetic tunnel junction device includes a first magnetic layer, a tunneling barrier layer provided on the first magnetic layer, and a second magnetic layer provided on the tunneling barrier layer. The method can include etching a portion of the second magnetic layer and a portion of the first magnetic layer by irradiating gas clusters onto a portion of a surface of the second magnetic layer or a portion of a surface of the first magnetic layer.