MRAM MTJ Stack Formation Using CMP Stop Layers

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Solution Overview

Problem

Current semiconductor memory technologies, specifically magnetoresistive random access memory (MRAM) devices, face challenges in efficiently forming and integrating magnetic tunnel junction (MTJ) stacks and interconnect structures due to limitations in etching and polishing processes, which affect the accuracy and reliability of magnetic memory cell formation.

Innovation Solution

The method involves forming a magnetic tunnel junction stack with a seed layer, ferromagnetic pinned and free layers, and a capping layer, followed by a dual-damascene process for interconnect structure formation, using chemical mechanical polishing (CMP) and etching techniques to achieve precise control over layer thickness and structure alignment, and incorporating CMP stop layers to prevent damage during polishing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional etching and polishing processes are used for MTJ stack formation, then manufacturing simplicity is maintained, but manufacturing precision and reliability deteriorate

Engineering Contradiction:

ImproveMTJ stack formation accuracyVSAvoidetching and polishing process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

CMP stop layers are deposited on the substrate before forming the MTJ stack, establishing protective reference surfaces in advance that prevent damage during subsequent polishing operations and ensure precise thickness control of interconnect layers

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The fabrication process is divided into distinct stages with separate CMP and etching operations, each targeting specific layers with predetermined stop layers, allowing precise control of each interface without affecting other structures

Inventive Principle:

Principle #1Segmentation

2Productivity

If aggressive polishing is used to remove excess materials, then productivity is improved, but reliability deteriorates due to potential damage to underlying structures

Engineering Contradiction:

Improvematerial removal efficiencyVSAvoidstructural integrity during polishing

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

CMP stop layers are deposited beforehand to cushion and protect the MTJ stack and other sensitive structures during aggressive polishing operations, allowing high productivity without compromising reliability

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The CMP stop layer acts as an intermediary between the polishing head and the underlying sensitive structures, absorbing mechanical stress and preventing direct damage while enabling efficient material removal

Inventive Principle:

Principle #24Intermediary (Mediator)

3Manufacturing precision

If precise control over layer thickness is achieved through multiple CMP steps, then manufacturing precision is improved, but loss of time increases

Engineering Contradiction:

Improvelayer thickness controlVSAvoidfabrication process time

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

Multiple CMP stop layers are deposited at predetermined stages before the MTJ stack formation, enabling precise thickness control of each interconnect layer in a systematic sequence that minimizes unnecessary iterations and reduces overall fabrication time

Inventive Principle:

Principle #10Preliminary action

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 the accuracy and reliability of MRAM device fabrication by ensuring precise control over MTJ stack formation and interconnect structures, improving the magnetic memory cell's performance and compatibility with back-end-of-line (BEOL) processing.

Implementation Method 1

using chemical mechanical polishing (CMP) and etching techniques to achieve precise control over layer thickness and structure alignment

Methodology Applied

Scientific EffectChemical mechanical polishing:

Implementation Method 2

using chemical mechanical polishing (CMP) and etching techniques to achieve precise control over layer thickness and structure alignment

Methodology Applied

Scientific EffectEtching:

Data Source

PatentUS11217627B2Magnetic random access memory device and formation method thereof

Publication Date: 2022.01.04 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method of forming a MRAM device includes forming an interconnect structure spanning a memory region and a peripheral region; forming a MTJ stack over the interconnect structure within the memory region; depositing a dielectric layer over the MTJ stack and spanning the memory region and the peripheral region; removing a first portion of the dielectric layer from the peripheral region, while leaving a second portion of the dielectric layer within the memory region; after removing the first portion of the dielectric layer from the peripheral region, forming a first IMD layer spanning the memory region and the peripheral region; forming a dual damascene structure through the first IMD layer to a metallization pattern of the interconnect structure within the peripheral region; and after forming the dual damascene structure within the peripheral region, forming a top electrode via in contact with a top electrode of the MTJ stack.