Crystalline Ruthenium CAP Layer Suppresses Boron Diffusion in MTJ Devices

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Solution Overview

Problem

Conventional MRAM manufacturing processes often result in MTJ devices with suboptimal operating characteristics due to etching damage and material diffusion, leading to variations in write current and coercive force, which are difficult to accurately set.

Innovation Solution

A laminated structure is implemented for MTJ devices, where the upper magnetic film contains boron and the tunnel insulating film is noncrystalline, with a CAP layer of crystalline ruthenium and a hard mask of tantalum, which suppresses boron diffusion and etching damage, thereby maintaining noncrystallinity and reducing write current variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional MRAM manufacturing processes are used, then MTJ devices can be produced, but etching damage and material diffusion occur leading to suboptimal operating characteristics

Engineering Contradiction:

Improveoperating characteristicsVSAvoidetching damage and material diffusion

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A CAP layer made of crystalline ruthenium is introduced as an intermediary between the upper magnetic film and the tunnel insulating film. This CAP layer serves as a protective mediator that suppresses boron diffusion from the upper magnetic film to the tunnel insulating film during manufacturing processes, thereby preventing etching damage and maintaining optimal operating characteristics of the MTJ device

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent employs a composite laminated structure consisting of multiple materials with specific properties: noncrystalline tunnel insulating film, upper magnetic film containing boron, and crystalline ruthenium CAP layer. This composite structure leverages the beneficial properties of each material to achieve both protection against diffusion and maintenance of magnetic characteristics

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If the upper magnetic film contains boron to improve magnetic properties, then coercive force can be optimized, but boron diffusion to the tunnel insulating film occurs causing variations in write current

Engineering Contradiction:

Improvecoercive force controlVSAvoidwrite current consistency

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

The crystalline ruthenium CAP layer acts as a diffusion barrier intermediary that prevents boron atoms from migrating from the upper magnetic film to the tunnel insulating film. This intermediary layer maintains the compositional stability of both the magnetic film and tunnel insulator, ensuring consistent write current while allowing the upper magnetic film to contain boron for optimized coercive force

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the physical state parameter of the CAP layer from amorphous to crystalline form. This crystalline structure provides superior diffusion barrier properties compared to amorphous materials, effectively blocking boron diffusion while maintaining the desired magnetic and electrical characteristics of the MTJ device

Inventive Principle:

Principle #35Parameter changes

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 enables the production of MTJ devices with improved operating characteristics by stabilizing the write current and accurately setting the coercive force, resulting in enhanced semiconductor performance.

Implementation Method 1

A CAP layer and a hard mask are laminated in this order over MTJ devices. The CAP layer contains a crystalline simple substance of Ru as a constituent material and the hard mask contains a Ta simple substance as a constituent material... suppresses boron diffusion

Methodology Applied

Scientific EffectDiffusion barrier: Diffusion Barrier

Implementation Method 2

the tunnel insulating film contains a noncrystalline constituent material... reducing etching damage, thereby maintaining noncrystallinity

Methodology Applied

Scientific EffectAmorphous structure resistance to etching:

Implementation Method 3

MTJ device is used as a concept including TMR (Tunneling Magneto Resistance) device... holds data by storing information in the spin of electrons

Methodology Applied

Scientific EffectMagnetic tunnel junction effect: Magnetoresistance

Data Source

PatentUS8383427B2Semiconductor device including a magnetic tunnel junction device including a laminated structure and manufacturing method therefor

Publication Date: 2013.02.26 RENESAS ELECTRONICS CORP

AI summary

A semiconductor device having a MTJ device excellent in operating characteristics and a manufacturing method therefor are provided. The MTJ device is formed of a laminated structure which is obtained by laminating a lower magnetic film, a tunnel insulating film, and an upper magnetic film in this order. The lower and upper magnetic films contain noncrystalline or microcrystalline ferrocobalt boron (CoFeB) as a constituent material. The tunnel insulating film contains aluminum oxide (AlOx) as a constituent material. A CAP layer is formed over the upper magnetic film and a hard mask is formed over the CAP layer. The CAP layer contains a substance of crystalline ruthenium (Ru) as a constituent material and the hard mask contains a substance of crystalline tantalum (Ta) as a constituent material. The film thickness of the hard mask is larger than that of the CAP layer.