EUV Photo Mask SRAFs Suppress Background Light

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Solution Overview

Problem

In extreme ultraviolet lithography (EUVL), EUV photo masks with high reflectivity absorber layers cause random printouts due to background light from absorber patterns, which existing technologies fail to effectively suppress, leading to reduced pattern accuracy and resolution.

Innovation Solution

The use of sub-resolution assist features (SRAFs) with periodic patterns having specific pitches and widths, integrated into the absorber layer of the EUV photo mask, suppresses background intensity by adjusting the pitch and line width of these patterns, preventing diffraction into the pupil and reducing random printouts.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If high reflectivity absorber layers are used in EUV photo masks, then signal contrast is improved, but random printouts occur due to background light from absorber patterns

Engineering Contradiction:

Improvesignal contrastVSAvoidbackground light causing random printouts

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The absorber layer is segmented into circuit patterns and sub-resolution assist patterns (SRAFs). The SRAFs are auxiliary structures with dimensions below the resolution limit that do not print but effectively suppress background light from the main circuit patterns, thereby reducing random printouts while maintaining signal contrast.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Sub-resolution assist patterns serve as intermediary elements between the circuit patterns and the background light. These SRAFs are strategically placed around circuit patterns and act as mediators to suppress background light through diffraction control, preventing it from causing random printouts on the wafer.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-generated harmful factors

If sub-resolution assist features with specific pitches and widths are introduced, then background intensity is suppressed and random printouts are reduced, but device complexity increases

Engineering Contradiction:

Improverandom printoutsVSAvoidmask pattern complexity

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The SRAFs are designed with specific dimensional parameters (width and pitch) that are below the resolution limit of the lithography system. By controlling these parameters, the SRAFs suppress background light through diffraction effects without being resolved as printed features, thus reducing random printouts while managing complexity through parameter optimization.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The SRAFs are placed in strategic locations around circuit patterns where background light suppression is most needed, rather than uniformly across the entire mask. This partial application of assist features focuses the complexity reduction effort on critical areas, achieving effective suppression of random printouts without unnecessarily increasing overall device complexity.

Inventive Principle:

Principle #16Partial or excessive action

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 implementation of SRAFs significantly enhances signal contrast, improves pattern accuracy, and suppresses defects in EUV photo masks, thereby improving the resolution and reliability of EUV lithography processes.

Implementation Method 1

suppresses background intensity by adjusting the pitch and line width of these patterns, preventing diffraction into the pupil

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

EUV photo masks with high reflectivity absorber layers cause random printouts due to background light from absorber patterns

Methodology Applied

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

Data Source

PatentUS20230314927A1EUV photo masks and manufacturing method thereof

Publication Date: 2023.10.05 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A photo mask for an extreme ultraviolet (EUV) lithography includes a circuit pattern, and sub-resolution assist patterns disposed around and connected to the circuit pattern. A dimension of the sub-resolution assist patterns is in a range from 10 nm to 50 nm.