EUV Attenuated Phase-Shifting Mask Absorber Layer Design

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Solution Overview

Problem

The semiconductor industry faces challenges in achieving higher feature resolution and density at increased wafer exposure throughput due to limitations in photolithography processes, particularly in extreme ultraviolet (EUV) lithography.

Innovation Solution

The introduction of a binary system absorber layer in an attenuated phase-shifting mask (APSM) used in EUV lithography, which manipulates the composition and thickness of the absorber layer to enhance image contrast and improve lithography resolution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional photomasks are used in EUV lithography, then the basic lithography function is maintained, but image contrast is insufficient and lithography resolution cannot be improved

Engineering Contradiction:

Improvelithography resolutionVSAvoidimage contrast

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent changes the optical parameters of the photomask by introducing an attenuating layer with specific thickness (5-50 nm) and material composition. This layer modifies the phase and amplitude of reflected EUV light, transforming the binary mask into an attenuated phase-shifting mask that achieves higher image contrast and improved lithography resolution through controlled parameter modification rather than fundamental design changes

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite structure consisting of multiple functional layers: a reflective base layer, an attenuating layer with specific optical properties, and a protective capping layer. This composite design combines the high reflectivity of the base layer with the phase-shifting capability of the attenuating layer, achieving superior image contrast and resolution that neither layer could provide alone

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If the numerical aperture (NA) of the EUV scanner is increased to improve resolution, then lithography resolution improves, but the complexity and cost of the lithography system increases

Engineering Contradiction:

Improvelithography resolutionVSAvoidNA of EUV scanner

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical/optical approach of increasing scanner NA with a mask-based solution. By incorporating an attenuating layer that modifies light phase and amplitude directly at the mask level, the system achieves improved resolution through material and optical property modifications rather than increasing the numerical aperture of the projection optics, thereby avoiding the associated complexity and cost increases

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If the absorber layer thickness is increased to improve image contrast, then image contrast improves, but the absorber layer becomes too thick for optimal EUV lithography operations

Engineering Contradiction:

Improveimage contrastVSAvoidabsorber layer thickness

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The patent optimizes the thickness parameter of the attenuating layer to fall within the specific range of 5-50 nm. This precise parameter control allows the layer to provide sufficient phase-shifting and amplitude modulation for high image contrast while maintaining optimal EUV light transmission and avoiding the detrimental effects of excessive thickness such as increased absorption and reduced throughput

Inventive Principle:

Principle #35Parameter changes

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 effectively improves image contrast and lithography resolution without the need to increase the numerical aperture (NA) of the EUV scanner, allowing for thinner absorber layers that are more suitable for EUV lithography operations.

Implementation Method 1

A first reflected light and a second reflected light from the absorber layer have a phase shift between about 1.1π and about 1.3π

Methodology Applied

Scientific EffectPhase shift: Interference

Implementation Method 2

The absorber layer includes a first material and a second material different from the first material

Methodology Applied

Scientific EffectAbsorption: Absorption (EM radiation)

Data Source

PatentUS20250036021A1Extreme ultraviolet lithography method and EUV photomask

Publication Date: 2025.01.30 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

An attenuated phase-shifting mask (APSM) includes a substrate, a multi-layer structure, a capping layer and an absorber layer. The substrate has a first side and a second side opposite to the first side. The multi-layer structure is disposed over the first side of the substrate. The capping layer is disposed over the multi-layer structure. The absorber layer is disposed over a portion of the capping layer. The absorber layer includes a first material and a second material different from the first material. A thickness of the absorber layer is between approximately 30 nm and approximately 65 nm. A refractive index (n) of the absorber layer is between approximately 0.860 and approximately 0.945. An extinction coefficient (k) of the absorber layer is between approximately 0.070 and approximately 0.015.