Linear Variable Filter Illumination System for Metrology Wavelength Selection

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Current metrology apparatuses in lithographic processes have limited flexibility in wavelength selection, typically allowing only discrete wavelengths, which restricts their ability to accurately measure properties of targets in different layers, and the switching time between wavelengths is slow, limiting measurement efficiency.

Innovation Solution

The implementation of a linear variable filter arrangement in the illumination system allows for continuous and rapid selection of wavelengths across a wide range, from 400 nm to 900 nm, using one or more linear variable filters that can be moved relative to the radiation beam, enabling faster and more precise wavelength adjustment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If discrete wavelength filters are used in metrology apparatus, then wavelength selection is possible, but flexibility in wavelength selection is limited and switching time between wavelengths is slow

Engineering Contradiction:

Improvewavelength selection flexibilityVSAvoidwavelength switching time

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The patent changes the fundamental parameter of wavelength selection from discrete filter switching to continuous spectral filtering using a linear variable filter. The filter's transmission characteristic varies linearly across its surface, allowing any wavelength within the filter's range to be selected by positioning the radiation beam at different locations across the filter surface, thereby achieving both high flexibility and fast switching.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical system of physically switching between multiple discrete filter elements with a positional control system that moves the radiation beam across a single continuous linear variable filter. This substitution eliminates the mechanical switching time associated with moving between separate filter components while maintaining wavelength selection capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If multiple discrete filters are used to cover a wide wavelength range, then wavelength coverage is improved, but device complexity increases

Engineering Contradiction:

Improvewavelength range coverageVSAvoidfilter arrangement complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The linear variable filter serves multiple functions simultaneously: it provides continuous wavelength selection across a broad spectral range, acts as a tunable bandpass filter, and enables rapid wavelength switching. A single linear variable filter component replaces what would traditionally require multiple discrete filter elements, reducing overall system complexity while maintaining or enhancing functional capabilities.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If wavelength-tuned measurement radiation is used for different targets, then measurement accuracy is improved, but measurement time increases due to individual tuning requirements

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidmeasurement throughput

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The system implements dynamic wavelength selection where the radiation beam's position across the linear variable filter can be rapidly adjusted during measurements. This dynamic positioning capability allows the system to quickly switch between wavelengths optimized for different target layers without the time penalty of physical filter changes, thereby maintaining high measurement accuracy across multiple targets while preserving measurement throughput.

Inventive Principle:

Principle #15Dynamics

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 solution enhances measurement accuracy and throughput by allowing multiple wavelength measurements on a single target, optimizing measurements for each layer and improving robustness against process variations, potentially doubling the accuracy and throughput compared to existing systems.

Implementation Method 1

a linear variable filter arrangement configured to filter a radiation beam from said illumination source and comprising one or more linear variable filters

Methodology Applied

Scientific EffectLinear variable filter: Filter (optical)

Data Source

PatentUS10416567B2Illumination system and metrology system

Publication Date: 2019.09.17 ASML NETHERLANDS BV

AI summary

Disclosed is an illumination system for a metrology apparatus and a metrology apparatus comprising such an illumination system. The illumination system comprises an illumination source; and a linear variable filter arrangement configured to filter a radiation beam from said illumination source and comprising one or more linear variable filters. The illumination system is operable to enable selective control of a wavelength characteristic of the radiation beam subsequent to it being filtered by the linear variable filter arrangement.