Lithography Mask Linewidth Fluctuation Analysis

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Solution Overview

Problem

Current methods fail to separate the structure-independent contribution of a lithography mask to linewidth fluctuation, which is crucial for determining the minimum achievable feature size and quality of lithography masks, as existing techniques cannot distinguish between imaging aberration and mask structure contributions in speckle patterns.

Innovation Solution

A method involving a focus stack measurement of a structure-free region, evaluating 2D intensity distributions through Fourier transformations and linear algebra to isolate the structure-independent optical surface roughness, allowing for the separation of imaging aberration contributions and determination of the minimum achievable linewidth fluctuation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional linewidth measurement methods are used, then general mask quality assessment is possible, but the structure-independent contribution to linewidth fluctuation cannot be separated from mask structure contributions

Engineering Contradiction:

Improvelinewidth fluctuation measurementVSAvoidseparation of imaging aberration and mask structure contributions

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent segments the total linewidth fluctuation into two distinct components: structure-independent contribution (imaging aberrations) and structure-dependent contribution (mask structure). This is achieved by measuring speckle patterns in both structured and unstructured regions of the mask, then mathematically separating the contributions through comparison and analysis of the respective intensity distributions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces speckle pattern analysis as an intermediary measurement technique. By using speckle patterns formed by coherent light illumination, the system creates an intermediate representation that encodes information about both imaging aberrations and mask structures, which can then be decoded to separate the two contributions through appropriate mathematical processing.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If focus stack measurement of structure-free regions is performed, then structure-independent contribution can be determined, but measurement time and process complexity increase

Engineering Contradiction:

Improvestructure-independent contribution determinationVSAvoidmeasurement time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent merges the measurement of structured and unstructured regions into a single integrated process. By recording focus stacks from both regions using the same optical setup and processing workflow, the method eliminates the need for separate measurement procedures, thereby reducing overall measurement time while maintaining the ability to separate contributions.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The measurement system is designed to perform multiple functions simultaneously: it characterizes both structured mask regions (for mask quality assessment) and unstructured regions (for imaging aberration determination) using the same optical path, illumination conditions, and detection system, making the process efficient and versatile.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If speckle pattern analysis is used to separate imaging aberration contributions, then mask quality assessment is improved, but evaluation complexity increases

Engineering Contradiction:

Improvemask quality assessmentVSAvoidevaluation process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces complex physical measurement setups with computational analysis methods. Instead of using separate optical systems to measure imaging aberrations and mask structures independently, the invention uses computational processing of speckle pattern images to extract both types of information, substituting mechanical/optical complexity with algorithmic processing.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the analysis parameters by working in the spatial frequency domain through Fourier transformation of the speckle patterns. This parameter transformation allows the separation of imaging aberration contributions from mask structure contributions through spectral analysis, making the evaluation more systematic and less complex than direct spatial domain analysis.

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

Enables the determination of a structure-independent contribution to linewidth fluctuation, improving lithography mask quality and process monitoring by identifying and reducing imaging aberrations, thereby enhancing the production of smaller features on wafers.

Implementation Method 1

evaluating the intensity variations attributable to so-called speckles in the aerial images of the lithography mask

Methodology Applied

Scientific EffectSpeckle pattern formation: Interference

Data Source

PatentUS11061331B2Method for determining a structure-independent contribution of a lithography mask to a fluctuation of the linewidth

Publication Date: 2021.07.13 CARL ZEISS SMT GMBH

AI summary

For determining a structure-independent contribution of a lithography mask to a fluctuation of the linewidth, recorded 2D intensity distributions (15zi) of an unstructured measurement region of a lithography mask are evaluated in a spatially resolved manner.