Strained Silicon Cleaning via Aqueous Ozone

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Solution Overview

Problem

Current RCA cleaning methods for strained silicon wafers after selective etching of SiGe layers etch the strained silicon layer, leading to surface roughness and thickness issues due to ammoniacal solutions, which are not effectively addressed in maintaining the integrity of the final product.

Innovation Solution

Aqueous ozone solution is used for cleaning the strained silicon layer post-selective etching, eliminating particulate contamination and surface defects without etching the silicon layer, utilizing single wafer type equipment for efficient propagation and concatenated with selective etching steps.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If RCA cleaning solution (SC1) is used to clean the strained silicon layer, then particulate contamination and surface defects are removed, but the strained silicon layer is etched, increasing surface roughness and reducing thickness

Engineering Contradiction:

Improvesurface cleanlinessVSAvoidsurface roughness

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent changes the chemical composition parameters of the cleaning solution by replacing ammonium hydroxide with organic solvents (acetone, isopropyl alcohol) and adjusting the temperature range to room temperature or slightly elevated temperatures, thereby eliminating etching while maintaining cleaning effectiveness

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful etching effect of ammonium hydroxide into a beneficial non-etching cleaning process by using organic solvents that can remove organic contaminants and particles without chemically attacking the strained silicon layer, thus protecting the layer integrity while achieving cleanliness

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Reliability

If RCA cleaning solution (SC1) is used to clean the strained silicon layer, then particles are removed from the surface, but the strained silicon layer thickness is reduced

Engineering Contradiction:

Improveparticle removalVSAvoidlayer thickness

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent changes the chemical composition parameters by substituting ammonium hydroxide with organic solvents (acetone, isopropyl alcohol) that have different chemical properties - they dissolve organic contaminants and lift particles through solvation rather than chemical etching, thus removing particles while preserving layer thickness

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces organic solvents as intermediary substances that mediate between the cleaning objective and the strained silicon layer - these solvents interact with particles and organic contaminants to remove them without directly attacking the silicon layer, thus achieving particle removal without thickness loss

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If standard RCA cleaning is performed, then the surface becomes hydrophilic and particles are removed, but metallic contaminants are not effectively removed and etching occurs

Engineering Contradiction:

Improveparticle removalVSAvoidmetallic contamination

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent uses a composite cleaning approach combining multiple organic solvents (acetone, isopropyl alcohol) with oxygen plasma treatment - the solvents remove organic contaminants and particles through dissolution, while the oxygen plasma removes metallic contaminants through oxidation, achieving comprehensive cleaning without etching

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent replaces the chemical etching mechanism of RCA cleaning with a combination of solvation (organic solvents dissolving contaminants) and oxidation (oxygen plasma reacting with metallic contaminants), thereby achieving contaminant removal through different chemical mechanisms that do not attack the strained silicon layer

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 aqueous ozone solution significantly reduces surface roughness and particle density, achieving a root mean square roughness of less than 1 Å and particle density of less than 3.2 particles/cm², while avoiding etching of the strained silicon layer, thus meeting tight constraints for sSOI product quality.

Implementation Method 1

a step of cleaning the surface of the strained silicon layer with an aqueous ozone solution

Methodology Applied

Scientific EffectOxidation: Oxidation

Data Source

PatentUS7439189B2Surface treatment after selective etching

Publication Date: 2008.10.21 SOITEC SA

AI summary

The invention concerns a method of treating wafers comprising at least one surface layer of silicon-germanium (SiGe) and a layer of strained silicon beneath the SiGe layer. The strained silicon layer is denuded by a step of selective etching of the SiGe layer by dispensing an etching solution onto the rotating wafer. Selective etching is then followed by a step of cleaning the surface of the strained silicon layer with an aqueous ozone solution dispensed onto the rotating wafer.