EUV Photomask Defect Repair via Diffraction-Based Phase Compensation

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Solution Overview

Problem

Current methods fail to effectively repair defects in photolithographic masks for the extreme ultraviolet (EUV) wavelength range, particularly buried defects in the multilayer structure, which hinder the precision and quality of semiconductor production.

Innovation Solution

A diffraction-based method for repairing defects, involving the determination of a repair shape that compensates for phase disturbances, using an imaging structure like a Fresnel zone plate and adjustments to the absorber pattern, to correct both phase and amplitude disturbances without modifying the multilayer mirror structure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional repair methods are used on EUV photomasks, then the multilayer mirror structure can be modified, but the repair effectiveness is insufficient and cannot properly correct phase disturbances caused by buried defects

Engineering Contradiction:

Improvedefect correction effectivenessVSAvoidrepair method complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces conventional mechanical/chemical repair approaches with an optical diffraction-based method. By depositing a diffraction optical element that generates corrective wavefronts, the system optically compensates for phase disturbances without physically modifying the multilayer mirror structure, thereby achieving effective defect correction while preserving the original mask architecture

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the optical parameters of the system by introducing a diffraction optical element with specific phase modulation characteristics. This element alters the wavefront propagation to compensate for defect-induced phase errors, achieving correction through parameter optimization rather than structural modification

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If the multilayer mirror structure is modified to repair defects, then visible defects may be addressed, but buried defects causing phase disturbances cannot be effectively corrected

Engineering Contradiction:

Improvemask surface qualityVSAvoidoptical performance consistency

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent introduces a diffraction optical element as an intermediary component that mediates between the defective multilayer mirror structure and the incident EUV radiation. This intermediary generates corrective diffraction patterns that compensate for phase disturbances caused by buried defects, allowing the original mirror structure to remain unchanged while achieving optical performance restoration

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent creates an optical copy or replica of the corrective phase modulation needed to compensate for defects. The diffraction optical element essentially copies the required phase correction pattern and applies it through diffraction, rather than directly modifying the original mirror surface

Inventive Principle:

Principle #26Copying

3Ease of repair

If repair processes modify the multilayer structure, then defect correction may be achieved, but the risk of introducing new defects or altering optical properties increases

Engineering Contradiction:

Improvedefect correction capabilityVSAvoidrisk of new defects

Core Design Contradiction:

Ease of repairVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the repair function from the multilayer mirror structure itself and separates it into an independent diffraction optical element. By taking out the phase correction functionality and implementing it through a separate deposited layer, the method enables defect correction without subjecting the sensitive multilayer structure to damaging repair processes

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent performs preliminary deposition of the diffraction optical element in a controlled manner, designing the element in advance to provide exact phase compensation. This preliminary action establishes the corrective mechanism before any potential damage could occur, allowing precise control over the repair process without introducing new defects

Inventive Principle:

Principle #10Preliminary action

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 enables precise correction of defects, ensuring high-quality EUV photomasks by restoring the original optical performance and preventing further defects during the repair process.

Implementation Method 1

the repair shape is diffraction-based in order to take account of a phase disturbance by the at least one defect

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS11774848B2Method and apparatus for repairing defects of a photolithographic mask for the EUV range

Publication Date: 2023.10.03 CARL ZEISS SMT GMBH

AI summary

The invention relates to a method and an apparatus for repairing at least one defect of a photolithographic mask for the extreme ultraviolet (EUV) wavelength range, wherein the method includes the steps of: (a) determining the at least one defect; and (b) ascertaining a repair shape for the at least one defect; (c) wherein the repair shape is diffraction-based in order to take account of a phase disturbance by the at least one defect.