EUV Mask Cleaning with Chilled SPM Solution

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Solution Overview

Problem

Existing methods for repairing photomasks in EUV lithography are ineffective and can introduce additional defects, particularly due to the exothermic reaction of sulfuric peroxide mixture (SPM) which damages the capping layer and introduces oxidation, leading to cracking and removal of the ruthenium layer.

Innovation Solution

A cooling module is used to rapidly chill the SPM solution to a non-thermal working temperature below room temperature, forming a fresh and cool cleaning solution that reduces oxidation and cracking of the capping layer while maintaining cleaning effectiveness, and a localized etching process is employed to remove hard defects without damaging the mask.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If sulfuric peroxide mixture (SPM) is used for cleaning the photomask, then cleaning effectiveness is improved, but the exothermic reaction causes oxidation and cracking of the capping layer

Engineering Contradiction:

Improvecleaning effectivenessVSAvoidoxidation and cracking of capping layer

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the temperature parameter of the SPM solution from ambient/exothermic conditions to sub-ambient temperatures (e.g., 4°C to 25°C). This parameter change suppresses the exothermic reaction that causes oxidation and cracking, while maintaining the cleaning effectiveness of the sulfuric peroxide mixture against soft defects on the photomask.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies preliminary cooling to the SPM solution before it contacts the photomask. By pre-chilling the solution to sub-ambient temperatures, the harmful exothermic reaction is counteracted in advance, preventing oxidation and cracking of the capping layer before they can occur during the cleaning process.

Inventive Principle:

Principle #9Preliminary anti-action

2Ease of manufacture

If conventional thermal cleaning methods are used, then cleaning process is simple, but additional defects are introduced to the photomask

Engineering Contradiction:

Improvecleaning process simplicityVSAvoidphotomask defect rate

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent introduces a temperature parameter change to sub-ambient conditions, which modifies the chemical reaction kinetics of the SPM solution. This reduces the aggressive oxidation effects that cause defects on the photomask, thereby improving manufacturing precision while maintaining process feasibility through the use of standard cooling equipment.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If SPM solution is applied at room temperature, then cleaning efficiency is high, but the capping layer damage increases

Engineering Contradiction:

Improvecleaning efficiencyVSAvoidcapping layer integrity

Core Design Contradiction:

ProductivityVSStrength

Solution Approach 1:

The patent changes the temperature parameter to sub-ambient levels, which slows down the chemical reaction rate of the SPM solution. This reduces the damage to the capping layer while maintaining adequate cleaning efficiency through extended contact time or optimized solution concentration, balancing productivity with component 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

The method effectively removes soft and hard defects from the photomask without damaging the capping layer, reducing oxidation and cracking, and maintaining the cleaning effectiveness, ensuring the integrity of the mask for precise lithography.

Implementation Method 1

the exothermic reaction of sulfuric peroxide mixture (SPM) which damages the capping layer and introduces oxidation

Methodology Applied

Scientific EffectExothermic reaction: Exothermic Reaction

Implementation Method 2

A cooling module is used to rapidly chill the SPM solution to a non-thermal working temperature below room temperature

Methodology Applied

Scientific EffectCooling: Cooling

Implementation Method 3

reducing oxidation and cracking of the capping layer

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 4

a localized etching process is employed to remove hard defects without damaging the mask

Methodology Applied

Scientific EffectEtching:

Data Source

PatentUS9665000B1Method and system for EUV mask cleaning with non-thermal solution

Publication Date: 2017.05.30 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

The present disclosure provides a method of repairing a mask. The method includes inspecting a mask to identify a defect on the mask; performing a cleaning process to the mask using a non-thermal chemical solution to the mask; and repairing the mask to remove the defect from the mask. The non-thermal chemical solution is cooled by a cooling module to a working temperature below room temperature.