MTJ Fabrication Using Etch Stop Layer for Offset Field Control

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Solution Overview

Problem

Current methods for fabricating Magnetic Tunnel Junction (MTJ) devices below 65 nm technology node face challenges in minimizing the offset field of the free layer, leading to scalability issues and non-uniformity in resistance, coercivity, and offset field, with inadequate etching stop methods causing damage to the reference layer.

Innovation Solution

A method involving the formation of a magnetic tunnel junction structure with a tunnel barrier layer and electrodes, using a dielectric hard mask to define the pinned layer before the free layer, followed by chemical mechanical polishing and a semiconductor damascene process to minimize etching damage and ensure uniformity, employing an etching stop on the tunnel barrier to control the dimensions and magnetic properties of the MTJ device.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of moving object

If the MTJ size is decreased to scale down devices, then device density increases, but the SAF reference layer becomes less effective at minimizing the offset field of the free layer

Engineering Contradiction:

ImproveMTJ device sizeVSAvoidoffset field control

Core Design Contradiction:

Area of moving objectVSReliability

Solution Approach 1:

The reference layer is segmented into two distinct parts: a SAF (synthetic antiferromagnetic) reference layer and a FM (ferromagnetic) reference layer. This segmentation allows each layer to perform different functions - the SAF layer provides magnetic anisotropy while the FM layer effectively minimizes the offset field, solving the problem of offset field control in scaled-down devices.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The reference layer uses a composite structure combining SAF and FM materials. The SAF component (e.g., CoFeB/MgO/CoFeB) provides perpendicular magnetic anisotropy, while the FM component (e.g., CoFeB) is engineered to minimize offset field coupling. This composite approach maintains effective offset field minimization even when overall device dimensions are reduced.

Inventive Principle:

Principle #40Composite materials

2Productivity

If conventional etching methods are used on the tunnel barrier, then the etching process can be completed, but etching damage occurs to the reference layer

Engineering Contradiction:

Improveetching process completionVSAvoidetching damage to reference layer

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

An etch stop layer (e.g., Ta or TaN) is deposited on the tunnel barrier before the main etching process. This preliminary action creates a protective interface that stops the etching process before it reaches the reference layer, preventing damage while allowing complete definition of the free layer pattern.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The etch stop layer acts as an intermediary between the tunnel barrier and the reference layer. It provides a controlled termination point for the etching process, allowing the etch to proceed through the tunnel barrier and free layer while stopping before damaging the sensitive reference layer structures.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If the offset field of the free layer is not minimized, then the magnetic properties can be maintained, but resistance uniformity and coercivity uniformity deteriorate

Engineering Contradiction:

Improvemagnetic propertiesVSAvoidresistance uniformity and coercivity uniformity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The reference layer is designed with spatially varying properties - the SAF portion provides local perpendicular anisotropy while the FM portion provides local offset field minimization. This local quality differentiation ensures uniform magnetic properties across the device while achieving low offset field values necessary for uniform resistance and coercivity.

Inventive Principle:

Principle #3Local quality

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 improves the uniformity of the free layer's resistance, coercivity, and offset field, reduces etching damage, and enhances the scalability of MTJ devices by maintaining better dimension control and minimizing tapered sidewall angles, resulting in improved yield and magnetic property control.

Implementation Method 1

a tunnel barrier layer between a free layer and a pinned layer

Methodology Applied

Scientific EffectQuantum tunneling:

Implementation Method 2

chemical mechanical polishing and a semiconductor damascene process

Methodology Applied

Scientific EffectChemical mechanical polishing:

Data Source

PatentUS8748197B2Reverse partial etching scheme for magnetic device applications

Publication Date: 2014.06.10 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A magnetic tunnel junction (MTJ) structure is provided over a device wherein the MTJ comprises a tunnel barrier layer between a free layer and a pinned layer; and a top and bottom electrode inside the MTJ structure. A hard mask layer is formed on the top electrode. The hard mask layer, top electrode, free layer, tunnel barrier layer, and pinned layer are patterned to define the magnetic tunnel junction (MTJ) structures. A first dielectric layer is deposited over the MTJ structures and planarized to expose the top electrode. Thereafter, the top electrode and free layer are patterned. A second dielectric layer is deposited over the MTJ structures and planarized to expose the top electrode. A third dielectric layer is deposited over the MTJ structures and a metal line contact is formed through the third dielectric layer to the top electrode to complete fabrication of the magnetic device.