EUV Reflective Mask Blank Absorber Stack for Low Stress and Roughness

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Solution Overview

Problem

Conventional reflective mask blanks for EUV lithography suffer from film stress and surface roughness issues in the absorber film, which affect pattern transfer accuracy and defect inspection sensitivity.

Innovation Solution

A reflective mask blank with an absorber film composed of multiple layers of tantalum (Ta) and nitrogen (N), including at least one low nitrogen content layer and one high nitrogen content layer, to achieve low film stress and surface roughness, optimized for EUV lithography.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a single-layer absorber film is used, then the manufacturing process is simple, but the film stress is large causing substrate warpage and the surface roughness is high

Engineering Contradiction:

Improveabsorber film formation processVSAvoidsubstrate surface flatness

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The absorber film is divided into multiple layers with different nitrogen contents (low nitrogen content layer and high nitrogen content layer). This segmentation allows each layer to contribute differently to stress management, reducing overall film stress and preventing substrate warpage while maintaining manufacturing feasibility.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the absorber film have different nitrogen contents tailored to specific functions: the low nitrogen content layer provides a foundation with lower stress, while the high nitrogen content layer enhances absorption performance. This local quality variation optimizes both stress distribution and optical performance.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If a single-layer absorber film is used, then the manufacturing process is simple, but the surface roughness is high reducing defect detection sensitivity

Engineering Contradiction:

Improveabsorber film formation processVSAvoiddefect detection sensitivity

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

Dividing the absorber film into multiple layers with controlled nitrogen contents reduces surface roughness. The low nitrogen content layer provides a smoother base structure, while the high nitrogen content layer maintains absorption efficiency, thereby improving defect detection sensitivity without complicating the manufacturing process excessively.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

By changing the nitrogen content parameter across different layers (from low to high), the film structure is optimized to reduce surface roughness. This parameter variation allows control over film morphology and stress, leading to a smoother surface that enhances defect detection capability.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If high nitrogen content is used in the absorber film, then the EUV light absorption is improved, but the film stress increases causing substrate deformation

Engineering Contradiction:

ImproveEUV light absorption performanceVSAvoidabsorber film stress

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The absorber film is segmented into layers with different nitrogen contents. The high nitrogen content layer provides excellent EUV light absorption, while the low nitrogen content layer counterbalances the stress. This segmentation allows the system to achieve high absorption performance without suffering from excessive film stress that would cause substrate deformation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different layers have locally optimized nitrogen contents: the high nitrogen content layer is positioned to maximize absorption where needed, while the low nitrogen content layer is structured to minimize stress accumulation. This local quality differentiation resolves the contradiction between absorption performance and stress management.

Inventive Principle:

Principle #3Local quality

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 solution provides a reflective mask with improved pattern transfer performance and enhanced sensitivity in defect inspection by reducing film stress and surface roughness, ensuring accurate pattern transfer in semiconductor manufacturing.

Implementation Method 1

a multilayer reflection film that reflects EUV light is formed on one of the two main surfaces of the substrate

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

an absorber film that absorbs EUV light is formed thereon

Methodology Applied

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

Data Source

PatentUS20260050206A1Reflective mask blank

Publication Date: 2026.02.19 SHIN ETSU CHEMICAL CO LTD

AI summary

A reflective mask blank including a substrate, a multilayer reflection film that is formed on the substrate and reflects exposure light, a protection film that is formed on the multilayer reflection film, and an absorber film that is formed in contact with the protection film and absorbs the exposure light is provided. The reflective mask blank is a material for a reflective mask used in EUV lithography using EUV light as the exposure light. The absorber film includes a main region that occupies not less than 94 % of a thickness of the absorber film, the main region consists of tantalum and nitrogen and is constituted of multiple layers that include at least one low nitrogen content layer having a nitrogen content of not more than 20 at %, and at least one high nitrogen content layer having a nitrogen content of 40 at % to 60 at %.