Composite Bottom Electrode Via for MRAM Resistance Reduction

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Solution Overview

Problem

Existing MRAM cell designs face performance degradation due to high-resistive bottom electrode vias, which increase additional resistance and hinder sensitivity and speed.

Innovation Solution

The use of a bottom electrode via comprising two different metals, copper and tungsten, where copper forms the majority of the lower portion and tungsten the upper portion, reduces overall resistance and prevents copper diffusion into the magnetic tunneling junction, thereby improving sensitivity and speed.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single-metal bottom electrode via is used, then the fabrication process is simple, but the series resistance is high which degrades memory circuit performance

Engineering Contradiction:

Improvememory circuit performanceVSAvoidvia structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The bottom electrode via is constructed using a composite material structure with a tungsten plug in the lower portion and a copper fill in the upper portion. The tungsten provides mechanical strength and diffusion barrier properties, while the copper provides low electrical resistance. This composite structure reduces series resistance by 60% to 90% compared to single-metal via structures, directly improving memory circuit performance without requiring fundamentally new fabrication processes.

Inventive Principle:

Principle #40Composite materials

2Reliability

If copper is used in the bottom electrode via, then the electrical resistance is reduced, but copper diffusion into the magnetic tunneling junction occurs which degrades device reliability

Engineering Contradiction:

Improveelectrical resistanceVSAvoidcopper diffusion

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The bottom electrode via is segmented into two distinct portions: a lower tungsten plug portion and an upper copper fill portion. The tungsten plug segment serves as a diffusion barrier that prevents copper atoms from migrating into the magnetic tunneling junction, while the copper fill segment provides low electrical resistance for current flow. This segmentation strategy successfully decouples the conflicting requirements of low resistance and diffusion prevention.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The tungsten plug acts as an intermediary material between the copper fill and the magnetic tunneling junction. It mediates the conflicting requirements by providing both a diffusion barrier function and electrical conductivity function, allowing copper to be used in the via structure without causing harmful diffusion effects. The tungsten plug thickness is specifically controlled to be greater than 50 nanometers to ensure adequate diffusion prevention.

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 configuration reduces the series resistance by 60% to 90%, enhancing the sensitivity and speed of MRAM cells while being compatible with existing semiconductor fabrication processes.

Implementation Method 1

The use of a bottom electrode via comprising two different metals, copper and tungsten, where copper forms the majority of the lower portion and tungsten the upper portion, reduces overall resistance

Methodology Applied

Scientific EffectElectrical Conduction: Conduction (electrical)

Implementation Method 2

tungsten the upper portion, reduces overall resistance and prevents copper diffusion into the magnetic tunneling junction

Methodology Applied

Scientific EffectDiffusion Barrier: Diffusion Barrier

Implementation Method 3

An MRAM cell is formed by a magnetic tunneling junction (MTJ) comprising two ferromagnetic layers which are separated by a thin insulating barrier, and operates by tunneling of electrons between the two ferromagnetic layers through the insulating barrier

Methodology Applied

Scientific EffectMagnetic Tunnel Effect:

Data Source

PatentUS20230389437A1Semiconductor memory device and method of forming the same

Publication Date: 2023.11.30 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A semiconductor device includes a substrate with a metal line embedded in the substrate, a dielectric layer disposed on the substrate, a bottom electrode via extending through the dielectric layer and landing on a top surface of the metal line, a bottom electrode disposed on a top surface of the bottom electrode via, a magnetic tunneling junction stack disposed on a top surface of the bottom electrode, and a top electrode disposed on the magnetic tunneling junction stack. A lower portion of the bottom electrode via includes a first metal, and an upper portion of the bottom electrode via includes a second metal that is different from the first metal.