Attenuated SRAF EUV Mask Resolution

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Solution Overview

Problem

Extreme ultraviolet (EUV) lithography faces challenges in printing smaller features due to the limitations of sub-resolution assist features (SRAFs) which are below the mask-writing resolution of present mask-making techniques, and the increasing numerical aperture reduces the process window for printing device patterns on semiconductor substrates.

Innovation Solution

A reflective patterning device with an absorber layer and a reflective layer that defines an attenuated sub-resolution assist feature (attenuated SRAF) is used, where the absorber layer and reflective layer together create a pattern layout with a main feature and an attenuated SRAF, allowing for improved resolution and manufacturing window by modifying the optical response to radiation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If sub-resolution assist features (SRAFs) are used to enhance main feature printing, then resolution is improved, but the SRAF widths become below the mask-writing resolution limit

Engineering Contradiction:

ImproveresolutionVSAvoidmask-writing capability

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent changes the optical parameters of the SRAF by introducing an attenuated phase-shift layer with specific transmittance (0.05-0.50) and optical thickness (0.01-0.25 micrometers). This transforms the SRAF from a simple geometric feature to an optical feature that achieves sub-resolution enhancement while remaining manufacturable with current mask-writing technology.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite patterning device structure combining multiple layers: a reflective layer, an absorber layer, and an attenuated phase-shift layer. This composite structure allows the SRAF to have different optical properties than the main features, enabling resolution enhancement without requiring the SRAF to be printed at their actual sub-resolution dimensions.

Inventive Principle:

Principle #40Composite materials

2Length of moving object

If numerical aperture is increased to print smaller features, then feature size is reduced, but the process window for printing decreases

Engineering Contradiction:

Improvefeature sizeVSAvoidprocess window

Core Design Contradiction:

Length of moving objectVSReliability

Solution Approach 1:

The patent modifies the optical parameters of the patterning device by introducing phase-shift layers with specific optical thickness and transmittance values. This changes the aerial image characteristics and intensity distribution, allowing smaller features to be printed while maintaining adequate process window through optimized optical contrast.

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

The attenuated SRAF enhances the resolution of main features on the substrate while avoiding the generation of features in the patterning material, thereby increasing the manufacturing process window and overcoming the limitations of current SRAF widths in EUV lithography.

Implementation Method 1

A reflective patterning device with an absorber layer and a reflective layer that defines an attenuated sub-resolution assist feature

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

an absorber layer and a reflective layer that together define a device pattern layout comprising an attenuated sub-resolution assist feature

Methodology Applied

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

Data Source

PatentUS11487198B2Patterning device, a method of making the same, and a patterning device design method

Publication Date: 2022.11.01 ASML NETHERLANDS BV

AI summary

A patterning device, includes: an absorber layer on a patterning device substrate; and a reflective or transmissive layer on the patterning device substrate, wherein the absorber layer and the reflective or transmissive layer together define a pattern layout having a main feature and an attenuated sub-resolution assist feature paired with the main feature, wherein: the main feature is configured to generate, upon transferring the device pattern to a layer of patterning material on a substrate, the main feature in the layer of patterning material, and upon the transferring the pattern to the layer of patterning material, the attenuated sub-resolution assist feature is configured to avoid generating a feature in the layer of patterning material and to produce a different radiation intensity than the main feature.