MRAM Contact Scheme Using CMP and RIE Segmentation

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Solution Overview

Problem

Establishing a top contact to magnetic tunnel junction (MTJ) devices while avoiding exposure to reactive plasma chemistries and ion bombardment, which can degrade device performance.

Innovation Solution

Employing a combination of selective chemical-mechanical planarization (CMP) and reactive ion etching (RIE) processes to uniformly contact MTJ devices across a wafer, using a dummy fill shape to maintain the height of MTJ devices and prevent exposure to harmful plasma chemistries.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional etching processes are used to establish top contact to MTJ devices, then contact formation is achieved, but device performance degrades due to exposure to reactive plasma chemistries and ion bombardment

Engineering Contradiction:

Improvedevice performanceVSAvoidexposure to reactive plasma chemistries and ion bombardment

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The etching process is segmented into multiple selective steps: first etching the oxide layer to expose the nitride layer, then etching the nitride layer to expose the MTJ device. This segmentation allows avoidance of harmful plasma chemistries by using mechanical polishing for the final exposure step, preventing direct ion bombardment of the MTJ device while still achieving contact formation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A dummy fill shape is introduced as an intermediary structure during the etching process. This dummy fill serves as a sacrificial element that protects the MTJ device from direct exposure to harmful plasma chemistries. The dummy fill is selectively removed in controlled steps, allowing contact formation without direct plasma exposure to the sensitive MTJ device.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If selective etching processes are used to expose MTJ device surfaces, then contact formation is achieved, but uniform contact across the wafer is difficult to maintain

Engineering Contradiction:

Improveuniform contact across waferVSAvoidprocess complexity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The process uses alternating CMP and RIE steps to maintain equipotential surfaces across the wafer. By periodically planarizing the surface with CMP between etching steps, the process ensures uniform exposure conditions across the entire wafer, compensating for any topography variations that would otherwise lead to non-uniform contact formation.

Inventive Principle:

Principle #12Equipotentiality

Solution Approach 2:

The manufacturing process employs periodic alternation between CMP (chemical-mechanical polishing) and RIE (reactive ion etching) steps. This periodic action allows controlled material removal while maintaining surface uniformity, ensuring that contact holes are exposed at consistent depths and positions across the entire wafer, thereby achieving uniform contact formation.

Inventive Principle:

Principle #19Periodic 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

Ensures consistent and reliable top contact formation to MTJ devices without adverse chemical interactions or ion damage, maintaining device performance and integrity.

Implementation Method 1

selective chemical-mechanical planarization (CMP) and reactive ion etch (RIE) processes

Methodology Applied

Scientific EffectChemical-mechanical planarization:

Implementation Method 2

selective etching, via a first etching process, an oxide layer to expose a top surface of a nitride layer

Methodology Applied

Scientific EffectReactive ion etching:

Data Source

PatentUS10644233B2Combined CMP and RIE contact scheme for MRAM applications

Publication Date: 2020.05.05 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A method is presented for establishing a top contact to a magnetic tunnel junction (MTJ) device, the method including selectively etching, via a first etching process, an oxide layer to expose a top surface of a nitride layer of a dummy fill shape and selectively etching, via a second etching process, a top portion of the nitride layer of the dummy fill shape to expose a top surface thereof. The method further includes selectively etching, via the second etching process, the oxide layer to expose a top surface of a nitride layer of the MTJ device, and selectively etching, via the first etching process, a top portion of the nitride layer of the MTJ device to expose a top surface thereof such that a height of the MTJ device is approximately equal to a height of the dummy fill shape.