Reflective EUV Masks with Embedded Absorbers for CD Control

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Solution Overview

Problem

EUV lithography masks face issues with damage to the backside conductive layer and three-dimensional effects causing critical dimension variation due to the absorber layer's height, which affect the precision of semiconductor manufacturing.

Innovation Solution

The EUV photo mask incorporates a reflective multilayer structure with an embedded absorber layer and an intermediate etching stop layer to suppress three-dimensional effects, using materials like Mo/Si and a capping layer to enhance durability and precision.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional photo mask structure is used in EUV lithography, then the mask can be manufactured with standard processes, but the backside conductive layer suffers damage and critical dimension variation occurs due to three-dimensional effects

Engineering Contradiction:

Improvemask durabilityVSAvoidcritical dimension precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The mask structure is segmented into multiple functional layers: a substrate layer, a reflective multilayer stack (Mo/Si alternating layers), an absorber layer with specific pattern, and a backside conductive layer. This segmentation allows each layer to perform its specific function independently, protecting the backside conductive layer while maintaining critical dimension precision through the reflective multilayer's optical properties

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The mask employs composite material structures including the reflective multilayer stack composed of alternating molybdenum and silicon layers, combined with the absorber layer containing EUV-absorbing materials. This composite structure achieves both durability for the backside conductive layer and precise critical dimension control through the optical properties of the multilayer stack

Inventive Principle:

Principle #40Composite materials

2Illumination intensity

If the absorber layer has significant height, then it provides sufficient EUV absorption contrast, but three-dimensional effects cause critical dimension variation

Engineering Contradiction:

ImproveEUV absorption contrastVSAvoidcritical dimension uniformity

Core Design Contradiction:

Illumination intensityVSManufacturing precision

Solution Approach 1:

The absorber layer is designed with spatially varying properties: in the patterned regions, it provides high EUV absorption contrast with optimized thickness, while in non-patterned regions, the reflective multilayer maintains its reflectivity. This local quality differentiation achieves sufficient absorption contrast where needed without creating three-dimensional effects that would cause critical dimension variation

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The absorber layer's thickness and material composition are precisely controlled to optimize EUV absorption contrast. By adjusting the absorber layer parameters (thickness, material density), sufficient contrast is achieved without excessive height that would cause three-dimensional effects and critical dimension variation

Inventive Principle:

Principle #35Parameter changes

3Productivity

If the reflective multilayer structure is used to enhance reflectivity, then EUV lithography efficiency improves, but the structure becomes more complex and difficult to manufacture

Engineering Contradiction:

Improvelithography efficiencyVSAvoidmask structure complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent extracts and separates the optical functionality into a dedicated reflective multilayer stack distinct from the absorber pattern layer. This extraction allows the multilayer stack to be optimized for reflectivity independently, improving lithography efficiency, while the absorber layer can be separately patterned to define the circuit geometry, simplifying the overall manufacturing process despite the enhanced structure

Inventive Principle:

Principle #2Taking out (Extraction)

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 configuration reduces damage to the backside conductive layer and minimizes critical dimension variation, ensuring high precision and reliability in EUV lithography processes.

Implementation Method 1

EUV lithography masks face issues with damage to the backside conductive layer and three-dimensional effects causing critical dimension variation

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

It is critical to fabricate EUV photo masks having a high contrast with a high reflectivity part and a high absorption part

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Data Source

PatentUS20250314956A1Reflective masks and methods of manufacturing semiconductor device

Publication Date: 2025.10.09 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A reflective mask includes a substrate, a lower reflective multilayer disposed over the substrate, an intermediate layer disposed over the lower reflective multilayer, an upper reflective multilayer disposed over the intermediate layer, a capping layer disposed over the upper reflective multilayer, and an absorber layer disposed in a trench formed in the upper reflective layers and over the intermediate layer. The intermediate layer includes a metal other than Cr, Ru, Si, Si compound and carbon.