Chalcogenide Memory Cell Fabrication with Sacrificial Layer Cleaning

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Solution Overview

Problem

Existing methods for fabricating phase change memory cells with chalcogenide materials face challenges in removing polymeric residues and treating damage regions, which can interfere with subsequent process stages and lead to device failure.

Innovation Solution

The use of improved cleaning procedures, including the formation and removal of a sacrificial silicon nitride layer at low temperatures to lift off polymeric residues, and the application of oxidants like hydrogen peroxide or nitric acid to treat damage regions, ensures effective removal of these issues.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional fabrication methods are used to form phase change memory cells with chalcogenide materials, then the basic device structure can be created, but polymeric residues and damage regions remain that interfere with subsequent process stages and lead to device failure

Engineering Contradiction:

Improvedevice reliabilityVSAvoidpolymeric residues and damage regions

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

A sacrificial silicon nitride layer is formed over the chalcogenide material layer before etching the memory cell structures. This preliminary action prepares the structure for subsequent cleaning by providing a layer that will be selectively removed to lift off polymeric residues. The sacrificial layer is deposited at low temperatures (below 300°C) to avoid damaging the temperature-sensitive chalcogenide material while still providing the necessary protective and sacrificial functions.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The sacrificial silicon nitride layer acts as an intermediary between the chalcogenide material layer and the polymeric residues. When the silicon nitride layer is selectively removed, it mediates the lifting off of polymeric residues from the chalcogenide material surface. This intermediary approach allows indirect removal of harmful residues without directly contacting or potentially damaging the sensitive chalcogenide material with harsh cleaning chemicals.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 3:

Oxidants such as hydrogen peroxide or nitric acid are applied to treat damage regions on the chalcogenide material layer. These strong oxidants accelerate the oxidation of damaged areas, effectively removing or neutralizing the harmful damage regions. The oxidants chemically react with the damaged material to restore or improve the quality of the chalcogenide layer, thereby enhancing device reliability.

Inventive Principle:

Principle #38Strong oxidants (Accelerated oxidation)

2Reliability

If low temperature deposition is used to form silicon nitride layer, then the chalcogenide material is protected from thermal damage, but the process requires precise temperature control and specialized equipment

Engineering Contradiction:

Improvechalcogenide material integrityVSAvoiddeposition process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The deposition temperature parameter is changed and constrained to be below 300°C for forming the silicon nitride sacrificial layer. This parameter change is critical because it protects the temperature-sensitive chalcogenide material from thermal damage while still allowing the silicon nitride to form with adequate quality. The low temperature parameter distinguishes this process from conventional high-temperature silicon nitride deposition and requires careful control, but ensures material integrity.

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 effectively removes polymeric residues and damage regions, preventing interference with subsequent process stages and enhancing the reliability of phase change memory cell fabrication.

Implementation Method 1

the formation and removal of a sacrificial silicon nitride layer at low temperatures to lift off polymeric residues

Methodology Applied

Scientific EffectLift-off:

Implementation Method 2

the application of oxidants like hydrogen peroxide or nitric acid to treat damage regions

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 3

Chalcogenide materials are capable of stably transitioning between amorphous and crystalline phases

Methodology Applied

Scientific EffectPhase change: Phase Change

Data Source

PatentUS9093641B2Methods of forming memory cells, and methods of patterning chalcogenide-containing stacks

Publication Date: 2015.07.28 MICRON TECHNOLOGY INC

AI summary

Some embodiments include methods of forming memory cells. Chalcogenide is formed over a plurality of bottom electrodes, and top electrode material is formed over the chalcogenide. Sacrificial material is formed over the top electrode material. A plurality of memory cell structures is formed by etching through the sacrificial material, top electrode material and chalcogenide. Each of the memory cell structures has a cap of the sacrificial material thereover. The etching forms polymeric residue over the sacrificial material caps, and damages chalcogenide along sidewalls of the structures. The sacrificial material is removed with an HF-containing solution, and such removes the polymeric residue off of the memory cell structures. After the sacrificial material is removed, the sidewalls of the structures are treated with one or both of H2O2 and HNO3 to remove damaged chalcogenide from the sidewalls of the memory cell structures.