EUV Photomask Capping Layer for Contamination Control

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Solution Overview

Problem

Existing EUV lithography techniques face challenges due to contamination by foreign particles, which affect the fidelity of circuit patterns and require frequent cleaning, leading to increased costs and reduced service life of photomasks.

Innovation Solution

A photomask with contaminant absorbers on its border and capping layers is introduced, designed to absorb and reduce the impact of contamination, utilizing materials like ruthenium and molybdenum-silicon layers to enhance contaminant absorption and reduce radiation absorption, thereby improving the operational cycle and efficiency of the lithography process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional photomask structures are used in EUV lithography, then the lithography process can proceed, but contamination accumulates on the photomask surface leading to reduced pattern fidelity and shortened service life

Engineering Contradiction:

Improvepattern fidelityVSAvoidcontamination accumulation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a capping layer as an intermediary between the multilayer stack and the external environment. This capping layer serves as a sacrificial barrier that absorbs contaminants, protecting the underlying optical layers and maintaining pattern fidelity throughout the photomask's service life.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The capping layer is designed as a consumable, sacrificial component that degrades preferentially to absorb contaminants. By sacrificing this relatively simple layer, the patent protects the more critical and expensive underlying multilayer stack, extending the overall photomask service life while maintaining optical performance.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If frequent cleaning of photomasks is performed to maintain pattern fidelity, then contamination is removed, but idle time increases and operational costs rise

Engineering Contradiction:

Improvepattern fidelityVSAvoididle time for cleaning

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The capping layer is pre-configured on the photomask before use, providing proactive contamination protection rather than requiring reactive cleaning. This preliminary protective measure prevents contaminant accumulation that would otherwise necessitate frequent cleaning interruptions, thereby reducing idle time and maintaining continuous operational efficiency.

Inventive Principle:

Principle #10Preliminary action

3Duration of action of stationary object

If the photomask structure is enhanced with additional contaminant-absorbing layers, then service life is extended and contamination is reduced, but device complexity increases

Engineering Contradiction:

Improvephotomask service lifeVSAvoidphotomask structure

Core Design Contradiction:

Duration of action of stationary objectVSDevice complexity

Solution Approach 1:

The patent segments the photomask structure into distinct functional layers: the multilayer stack for optical performance, the capping layer for contamination protection, and the absorber layer for additional contaminant absorption. This segmentation allows each layer to perform its specific function independently, extending service life through targeted protection without unnecessarily complicating the overall structure.

Inventive Principle:

Principle #1Segmentation

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 implementation of contaminant absorbers effectively reduces the accumulation of contaminants on the photomask, enhancing the lithography performance by maintaining pattern fidelity and extending the service life of the photomask, while also decreasing idle time and cleaning costs.

Implementation Method 1

a multilayer stack disposed over the substrate and configured to reflect a radiation beam

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

an absorber configured to absorb the foreign particles

Methodology Applied

Scientific EffectAbsorption: Absorption (physical)

Data Source

PatentUS11480869B2Photomask with enhanced contamination control and method of forming the same

Publication Date: 2022.10.25 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A photomask includes a substrate, a multilayer stack disposed over the substrate and configured to reflect a radiation, a capping layer over the multilayer stack, and an anti-reflective layer over the capping layer. The anti-reflective layer comprises a first pattern, wherein the first pattern exposes the capping layer and is configured as a printable feature. The photomask also includes an absorber spaced apart from the printable feature from a top-view perspective.