MTJ Critical Dimension Control Beyond Lithography Variation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

The existing fabrication methods for magnetoresistive random-access memory (MRAM) cells face challenges in achieving precise control over the magnetoresistive properties of the magnetic tunnel junction (MTJ) structure, leading to potential information read errors due to faulty read-out processes and inadvertent magnetization switching, especially in miniaturized elements where the digital '1' and '0' states differ by less than an order of magnitude.

Innovation Solution

The method involves forming a precisely defined hard mask with lithography-independent critical dimensions to control the lateral shape of the MTJ structure, using a sequence of etching steps and conformal layer deposition to define the MTJ area accurately, thereby minimizing variations and ensuring robust operation of MRAM cells.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional lithography methods are used to define MTJ structure dimensions, then manufacturing process simplicity is maintained, but manufacturing precision deteriorates due to lithography variation affecting critical dimension control

Engineering Contradiction:

Improvecritical dimension controlVSAvoidfabrication process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent transitions from defining MTJ critical dimensions in the lateral plane through lithography to defining them through vertical layer thickness control. The mandrel-less self-aligned process uses conformal deposition of layers (e.g., bottom electrode, magnetic layers, tunnel barrier, top electrode) where the critical dimension is determined by film thickness rather than lithographic patterning, thereby achieving lithography-independent dimensional control.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The self-aligned process inherently defines the MTJ critical dimensions through the sequential conformal deposition of layers around a void space, eliminating the need for external lithographic alignment. The structure self-organizes with precise dimensional control based on film thickness parameters, reducing reliance on lithography precision and alignment processes.

Inventive Principle:

Principle #25Self-service

2Productivity

If MTJ structure is miniaturized to increase storage density, then productivity is improved, but manufacturing precision deteriorates due to increased sensitivity to dimensional variations

Engineering Contradiction:

Improvestorage densityVSAvoiddimensional control

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

By controlling the critical dimensions through vertical film thickness rather than lateral lithographic patterning, the process enables precise control at smaller dimensions. The conformal deposition method maintains consistent thickness control even as the overall MTJ size is reduced to increase storage density, overcoming the increased sensitivity to dimensional variations in miniaturized structures.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Manufacturing precision

If lithography-based patterning is used to define MTJ area, then ease of manufacture is maintained, but manufacturing precision deteriorates due to read-out errors from dimensional variations

Engineering Contradiction:

ImproveMTJ area definitionVSAvoidpatterning process simplicity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The self-aligned mandrel-less process automatically defines the MTJ area through conformal layer deposition, eliminating the need for separate lithographic patterning steps. The critical dimension is self-determined by the film thickness parameters, providing precise MTJ area definition while maintaining ease of manufacture through a streamlined fabrication process.

Inventive Principle:

Principle #25Self-service

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 results in reliable and precise control over the magnetoresistive properties of MRAM cells, reducing inadvertent information read errors and ensuring reliable operation by maintaining accurate lateral dimensions of the MTJ structure, even in miniaturized forms.

Implementation Method 1

etching the interlayer with an at least partially isotropic etchant through the first opening

Methodology Applied

Scientific EffectEtching:

Implementation Method 2

etching the conformal layer and the transfer layer with an anisotropic etch to form a second opening

Methodology Applied

Scientific EffectAnisotropic etching:

Implementation Method 3

forming a conformal layer over the interlayer and the patterning layer to fill the first opening

Methodology Applied

Scientific EffectConformal deposition: Deposition (physical)

Implementation Method 4

depositing a hard mask material in the second opening

Methodology Applied

Scientific EffectMaterial deposition: Deposition (physical)

Data Source

PatentUS12058940B2Method for forming MTJS with lithography-variation independent critical dimension

Publication Date: 2024.08.06 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Some examples relate to an integrated circuit. The integrated circuit comprises a semiconductor substrate, a bottom electrode over the substrate, a circular magnetic tunneling junction (MTJ) disposed over an upper surface of bottom electrode, and a circular top electrode disposed over an upper surface of the magnetic tunneling junction. The circular top electrode is concentric to the circular magnetic tunneling junction, and a diameter of the circular magnetic tunneling junction is smaller than 60 nm or smaller than 30 nm.