Under-Cut Via Electrode Layout for Etchless Sub-60 Nm MRAM

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Solution Overview

Problem

The fabrication of magnetoresistive random-access memory (MRAM) devices involves precise patterning steps, including reactive ion etching (RIE), which can cause chemical damage and metal re-deposition on the sidewalls of magnetic tunneling junction (MTJ) cells, leading to performance issues.

Innovation Solution

A method for forming MTJ structures without chemical damage or metal re-deposition, involving the deposition of a first dielectric layer on a bottom electrode, partial etching to form a via opening with straight sidewalls, and subsequent etching to create a tapered via opening. A metal layer is deposited and the excess is removed, forming an electrode plug. MTJ stacks are deposited discontinuously on this plug and the bottom electrode, followed by the deposition of a second dielectric layer and a top electrode to complete the MTJ structure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If reactive ion etching (RIE) is used to pattern MTJ cells, then precise patterning and separation of MTJ cells is achieved, but chemical damage and metal re-deposition on sidewalls occurs leading to performance degradation

Engineering Contradiction:

Improvepatterning precisionVSAvoidchemical damage and metal re-deposition

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent segments the via formation process into two distinct steps: first forming a tapered via opening through the dielectric layer, then forming a separate metal electrode plug within that via. This segmentation allows the MTJ stack to be deposited discontinuously on the electrode plug without requiring plasma etching, thereby avoiding chemical damage and metal re-deposition on the MTJ sidewalls while maintaining precise patterning capability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of the conventional approach of etching the MTJ stack through plasma to define patterns, the patent inverts the sequence by first forming the electrode plug structure, then depositing the MTJ stack discontinuously on top of it. This inversion eliminates the need for plasma etching of the MTJ stack itself, preventing chemical damage and metal re-deposition on the sidewalls while achieving the desired sub-60 nm pattern dimensions

Inventive Principle:

Principle #13The other way round (Inversion)

2Object-affected harmful factors

If ion beam etching (IBE) is used to avoid chemical damage, then sidewall damage is reduced, but conductive materials are re-deposited into the tunnel barrier causing shorted devices

Engineering Contradiction:

Improvesidewall damageVSAvoiddevice shorting

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent extracts the patterning function from the MTJ stack etching process by forming the pattern definition through the dielectric layer and electrode plug structure beforehand. The MTJ stack is then deposited discontinuously on the pre-formed electrode plug, taking out the need for plasma or physical etching of the MTJ stack itself, thereby eliminating both chemical damage and metal re-deposition issues

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent inverts the conventional process sequence by forming the electrode plug first through a two-step via formation process, then depositing the MTJ stack discontinuously on top of it. This inversion eliminates the need for etching the MTJ stack with IBE or plasma, preventing both sidewall damage from physical sputtering and metal re-deposition into the tunnel barrier that would cause device shorting

Inventive Principle:

Principle #13The other way round (Inversion)

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 allows for the formation of sub-60 nm MTJ patterns without plasma etching, avoiding chemical damage and metal re-deposition, thereby improving the performance of MRAM devices.

Implementation Method 1

The first dielectric layer is partially etched through to form a first via opening having straight sidewalls. Then, the first dielectric layer is etched all the way through to the bottom electrode in the first via opening to form a second via opening wherein the second via opening has tapered sidewalls

Methodology Applied

Scientific EffectEtching:

Implementation Method 2

A metal layer is deposited over the first dielectric layer and in the second via opening

Methodology Applied

Scientific EffectDeposition: Deposition (physical)

Implementation Method 3

MTJ stacks are deposited on the electrode plug and on the bottom electrode wherein the MTJ stacks are discontinuous

Methodology Applied

Scientific EffectDeposition: Deposition (physical)

Data Source

PatentUS12207567B2Under-cut via electrode for sub 60nm etchless MRAM devices by decoupling the via etch process

Publication Date: 2025.01.21 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method for fabricating a magnetic tunneling junction (MTJ) structure is described. A first dielectric layer is deposited on a bottom electrode and partially etched through to form a first via opening having straight sidewalls, then etched all the way through to the bottom electrode to form a second via opening having tapered sidewalls. A metal layer is deposited in the second via opening and planarized to the level of the first dielectric layer. The remaining first dielectric layer is removed leaving an electrode plug on the bottom electrode. MTJ stacks are deposited on the electrode plug and on the bottom electrode wherein the MTJ stacks are discontinuous. A second dielectric layer is deposited over the MTJ stacks and polished to expose a top surface of the MTJ stack on the electrode plug. A top electrode layer is deposited to complete the MTJ structure.