EUV Reflective Mask Embedded Absorbers for Reduced CD Variation

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Solution Overview

Problem

EUV lithography masks face challenges due to three-dimensional effects and CD (critical dimension) variations caused by the height of the absorber layer, leading to damage and performance issues in reflective multilayer structures.

Innovation Solution

The absorber layer is embedded within a reflective multilayer structure, and an intermediate etching stop layer is introduced to suppress these effects, along with a capping layer to prevent oxidation and a backside conductive layer to enhance durability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the absorber layer height is increased to improve absorption, then absorption performance is improved, but three-dimensional effects and CD variations increase

Engineering Contradiction:

Improveabsorption performanceVSAvoidCD variation

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent embeds the absorber layer within trenches in the reflective multilayer structure, transitioning from a surface-level layer to a subsurface embedded configuration. This dimensional change allows the absorber to maintain effective absorption while reducing its protruding height that causes three-dimensional effects and CD variations.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The absorber layer is nested within trenches formed in the reflective multilayer structure, with the absorber fitting inside the recessed regions. This nesting approach allows the absorber to be surrounded by the reflective layers, maintaining optical functionality while minimizing surface height variations.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Reliability

If the absorber layer height is increased to improve absorption, then absorption performance is improved, but damage to the reflective multilayer structure increases

Engineering Contradiction:

Improveabsorption performanceVSAvoiddamage to reflective multilayer

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The patent introduces an intermediate etching stop layer beneath the absorber layer and uses capping layers to surround the embedded absorber structure. These protective layers are placed beforehand to cushion and protect the reflective multilayer structure from damage during fabrication and operation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Manufacturing precision

If an intermediate etching stop layer is introduced to suppress three-dimensional effects, then manufacturing precision is improved, but device complexity increases

Engineering Contradiction:

ImproveCD variationVSAvoidstructure complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The intermediate etching stop layer serves multiple functions: it acts as an etching stop during trench formation, provides a planarization surface, and serves as a foundation for the absorber layer. This multi-functionality reduces the need for additional separate layers and processes.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent combines the etching stop function with the intermediate layer that supports the absorber, merging multiple functions into a single layer rather than adding separate components. This integration reduces overall structural complexity while maintaining precision.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS12353120B2EUV photo masks and manufacturing method thereof

Publication Date: 2025.07.08 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.