Semiconductor Cleaning Liquid for Cobalt Corrosion Suppression

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Solution Overview

Problem

In semiconductor wafer processing, the thinning of Ta/TaN barrier metal layers due to miniaturization increases the risk of galvanic corrosion between copper and cobalt or ruthenium, leading to severe operation failures, and existing cleaning solutions fail to effectively suppress corrosion of cobalt or cobalt alloys during post-CMP or post-etch cleaning steps.

Innovation Solution

A cleaning liquid containing a surfactant such as polyoxyalkylene alkyl ether phosphoric acid and a chelating agent like serine, with a pH of 8 or more, and an oxidizing agent, is used to form an oxide film on cobalt surfaces, thereby suppressing corrosion and ensuring effective cleaning.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the Ta/TaN barrier metal layer is thinned to compensate for copper ion diffusion barrier properties, then the barrier property is improved, but the risk of galvanic corrosion increases

Engineering Contradiction:

Improvebarrier propertyVSAvoidgalvanic corrosion

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a cleaning liquid as an intermediary substance that contains specific components (surfactant, chelating agent, oxidizing agent) to mediate the interaction between copper and cobalt/ruthenium. This cleaning liquid forms a protective oxide film on the cobalt surface, preventing direct galvanic contact and corrosion while allowing the thin barrier metal layer to maintain its electrical barrier function.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the chemical environment parameters by adjusting the pH to 8 or more and incorporating specific chemical agents that alter the surface chemistry of cobalt. This parameter change enables the formation of a stable oxide film that protects against corrosion while maintaining the thinness of the barrier metal layer.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If cobalt or cobalt alloy is used as wiring or contact plug material, then the resistance value is reduced, but the corrosion resistance deteriorates

Engineering Contradiction:

Improveelectrical conductivityVSAvoidcorrosion resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent employs an oxidizing agent in the cleaning liquid that accelerates the oxidation of cobalt surface to form a stable oxide film. This strong oxidation creates a protective layer that prevents further corrosion of the cobalt material while maintaining its electrical conductivity properties.

Inventive Principle:

Principle #38Strong oxidants (Accelerated oxidation)

Solution Approach 2:

The oxide film formed on the cobalt surface acts as a sacrificial protective layer that can be easily formed and provides temporary protection during the cleaning process. This thin oxide layer prevents corrosion without significantly affecting the overall electrical performance of the cobalt wiring or contact plug.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Productivity

If conventional cleaning liquids are used for post-CMP cleaning, then the cleaning effect is achieved, but the corrosion of cobalt or cobalt alloy is not suppressed

Engineering Contradiction:

Improvecleaning effectVSAvoidcorrosion of cobalt

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent creates a composite cleaning liquid system combining multiple functional components: surfactants for general cleaning, chelating agents to bind metal ions, and oxidizing agents to form protective oxide films on cobalt. This composite formulation achieves both effective cleaning and corrosion suppression simultaneously.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The cleaning liquid is designed with multi-functionality, where the same formulation performs multiple tasks: removing abrasive particles and organic residues through surfactant action, binding metal ions through chelation, and forming protective oxide films on cobalt through oxidation. This universal approach eliminates the need for separate protective treatments.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 cleaning liquid effectively prevents corrosion of cobalt or cobalt alloys on semiconductor wafers, reducing the risk of operation failures and ensuring thorough cleaning post-CMP or post-etch processes.

Implementation Method 1

an oxidizing agent, is used to form an oxide film on cobalt surfaces, thereby suppressing corrosion

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 2

trace metal components such as derivatives eluted from the metal is present as residues on a surface of a semiconductor wafer after a CMP step or after an etching step, and these residues can be dissolved and removed with a chelating agent

Methodology Applied

Scientific EffectChelation:

Data Source

PatentUS11149231B2Cleaning liquid, cleaning method, and method for producing semiconductor wafer

Publication Date: 2021.10.19 MITSUBISHI CHEM CORP

AI summary

A cleaning liquid containing at least one surfactant (A) selected from the group consisting of a polyoxyalkylene alkyl ether phosphoric acid, a polyoxyalkylene alkyl ether acetic acid and a polyoxyalkylene alkyl ether sulfonic acid and a chelating agent (C), which has a pH of 8 or more, and a cleaning liquid containing an oxidizing agent (B) and a chelating agent (C), which has a pH of 8 or more.