Spin Torque MRAM Fabrication Using Negative Tone Lithography

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Solution Overview

Problem

Existing MRAM fabrication techniques face challenges in achieving uniformity and high yield, particularly at small sizes, resulting in non-functional devices with poor roundness and electrical property variations.

Innovation Solution

The use of negative-tone resist developer combined with positive resist or positive-tone developer and negative resist, along with a dark-field reticle, to form MRAM devices, employing complementary metal oxide semiconductor manufacturing techniques and ion beam etching for improved patterning and uniformity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If conventional positive-tone resist developer and positive resist with bright-field reticle are used, then the fabrication process is simple, but the critical dimension roundness and uniformity deteriorate

Engineering Contradiction:

Improvefabrication process simplicityVSAvoidcritical dimension roundness and uniformity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent inverts the conventional lithography approach by using negative-tone resist developer with positive resist or positive-tone developer with negative resist combined with dark-field reticle. This inversion of the development tone and reticle type fundamentally changes the patterning mechanism to achieve superior circularity and critical dimension uniformity while maintaining manufacturing feasibility

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes key lithography parameters including the tone of the resist developer, the type of resist material, and the illumination mode of the reticle. These parameter changes transform the patterning process from producing elliptical or irregular features to achieving highly uniform circular critical dimensions essential for high-density MRAM fabrication

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If patterning is performed at small sizes for high density, then storage capacity increases, but uniformity and yield deteriorate

Engineering Contradiction:

Improvestorage densityVSAvoidpatterning uniformity

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

By inverting the lithography approach to use negative-tone development with dark-field reticle, the patent achieves superior patterning uniformity at small feature sizes. This inverted approach creates more robust patterning control that maintains critical dimension uniformity even as feature sizes decrease to achieve higher storage densities

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent replaces conventional lithography mechanics with an enhanced patterning system that uses ion beam etching instead of traditional plasma etching. This substitution provides better anisotropy and etch uniformity, enabling precise patterning at small dimensions required for high-density MRAM while maintaining excellent uniformity across the wafer

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of manufacture

If conventional etching methods are used, then the process is straightforward, but the sidewall smoothness and roundness deteriorate

Engineering Contradiction:

Improveetching process simplicityVSAvoidsidewall smoothness and roundness

Core Design Contradiction:

Ease of manufactureVSShape

Solution Approach 1:

The patent replaces conventional plasma etching with ion beam etching, substituting a mechanical/physical sputtering process that offers superior control over etch profiles. This substitution produces highly smooth sidewalls and excellent circularity by providing more uniform material removal and better anisotropy, directly addressing the shape quality issues of conventional etching methods

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 patterning uniformity and yield, achieving superior results compared to conventional methods, with MRAM devices exhibiting circular cross-sections and improved smoothness, reducing error rates and increasing resistance distribution consistency.

Implementation Method 1

employing complementary metal oxide semiconductor manufacturing techniques and ion beam etching for improved patterning and uniformity

Methodology Applied

Scientific EffectIon beam etching: Ion Beam

Implementation Method 2

employ negative-tone resist developer combined with positive resist, or positive-tone developer and negative resist, with a dark-field reticle to form an MRAM device

Methodology Applied

Scientific EffectNegative-tone lithography:

Data Source

PatentUS10388857B2Spin torque MRAM fabrication using negative tone lithography and ion beam etching

Publication Date: 2019.08.20 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A magnetoresistive memory cell includes a magnetic tunnel junction pillar having a circular cross section. The pillar has a pinned magnetic layer, a tunnel barrier layer, and a free magnetic layer. A first conductive contact is disposed above the magnetic tunnel junction pillar. A second conductive contact is disposed below the magnetic tunnel junction pillar.