HfO2 Capping Layer Strategy for Low-Leakage Ferroelectric Films

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Solution Overview

Problem

High thermal budgets required for hafnium oxide (HfO2)-based ferroelectric random access memory (FeRAM) applications lead to increased leakage current and device degradation due to defect generation and film cracking, which degrades the ferroelectric properties of HfO2, especially when annealing temperatures exceed 600-650°C.

Innovation Solution

A method involving the use of a capping layer, such as silicon nitride (SiN) or silicon dioxide (SiO2), that does not include titanium or tantalum, to form ferroelectric HfO2 by annealing, followed by selective etching to remove the capping layer without diffusing atoms into the HfO2, and subsequent deposition of additional HfO2 to repair any cracking, thereby reducing defects and leakage current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high annealing temperatures (above 600-650°C) are used to form ferroelectric HfO2, then the ferroelectric properties are achieved, but leakage current increases and device degradation occurs due to defect generation and film cracking

Engineering Contradiction:

Improveferroelectric propertiesVSAvoidleakage current and defect generation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A capping layer comprising silicon nitride (SiN), silicon oxide (SiO2), or aluminum oxide (Al2O3) is deposited over the HfO2 layer before annealing. This intermediary layer prevents harmful interactions between the HfO2 and the environment during high-temperature processing, reducing defect generation and leakage current while allowing the ferroelectric phase to form at temperatures above 600-650°C

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The capping layer is deposited in advance before the high-temperature annealing process. This preliminary protective action prevents oxidation and contamination of the HfO2 layer during subsequent thermal processing, enabling reliable ferroelectric property formation without the harmful effects of direct environmental exposure

Inventive Principle:

Principle #10Preliminary action

2Reliability

If conventional PZT materials are used for ferroelectric memory, then adequate switching window is achieved, but the material cannot be used for thicknesses below 50 nanometers

Engineering Contradiction:

Improveswitching windowVSAvoidfilm thickness

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The invention changes the material system from conventional PZT to hafnium oxide (HfO2)-based materials, which exhibit different physical properties including higher coercive fields and superior scaling behavior. This parameter change in material composition enables ferroelectric switching functionality at thicknesses below 50 nm while maintaining adequate switching windows

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The capping layer is selectively applied only where needed to protect the thin HfO2 layer during processing, allowing the use of ultra-thin ferroelectric films without compromising their integrity. This localized protective approach enables the exploitation of HfO2's inherent ability to function at reduced thicknesses

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

The approach effectively forms ferroelectric HfO2 with reduced defects and leakage, maintaining its ferroelectric properties while preventing degradation caused by Ti diffusion, thus enhancing the thermal stability and reliability of HfO2-based FeRAM devices.

Implementation Method 1

annealing the HfO2 layer and the capping layer to form ferroelectric hafnium HfO2

Methodology Applied

Scientific EffectPhase transformation: Phase Change

Implementation Method 2

Annealing the HfO2 layer and the capping layer to form ferroelectric hafnium HfO2 includes performing a rapid thermal annealing process at a temperature within a range of 500 and 1000° C.

Methodology Applied

Scientific EffectRapid thermal annealing: Heat Treatment

Implementation Method 3

selectively etching the capping layer includes wet etching the capping layer using a diluted hydrofluoric acid solution

Methodology Applied

Scientific EffectWet etching:

Implementation Method 4

selectively etching the capping layer includes dry plasma etching the capping layer using a plasma generated with at least one of a fluorocarbon plasma and a halogen plasma

Methodology Applied

Scientific EffectPlasma etching: Plasma

Implementation Method 5

depositing additional HfO2 material onto the HfO2 layer

Methodology Applied

Scientific EffectMaterial deposition: Deposition (physical)

Data Source

PatentUS11923189B2Capping layer for a hafnium oxide-based ferroelectric material

Publication Date: 2024.03.05 LAM RES CORP

AI summary

A method of forming ferroelectric hafnium oxide (HfO2) in a substrate processing system includes depositing an HfO2 layer on a substrate, depositing a capping layer on the HfO2 layer, annealing the HfO2 layer and the capping layer to form ferroelectric hafnium HfO2, and selectively etching the capping layer to remove the capping layer without removing the HfO2 layer.