Lithography Mask Interference Metrology for Fast Inline Characterization
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Solution Overview
Problem
Existing methods for characterizing the optical properties of lithographic masks, such as atomic force microscopy (AFM), are slow and not informative enough for inline monitoring during mask manufacturing, and synchrotron EUV sources are difficult to deploy in the manufacturing process.
Innovation Solution
A mask characterization apparatus using an EUV light source, optical grating, and detector array to measure interference patterns, allowing for fast inline characterization of reflective and transmission masks by determining a quality metric based on interference signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If atomic force microscopy (AFM) is used to characterize masks, then measurement precision is improved, but productivity deteriorates due to slow characterization speed
Solution Approach 1:
The patent replaces the mechanical scanning approach of AFM with an optical interference measurement system. Instead of physically scanning the mask surface with a probe, the system uses EUV light interference patterns to characterize mask properties, enabling parallel measurement across the entire mask surface simultaneously, thus dramatically increasing characterization speed while maintaining precision
Solution Approach 2:
The patent transitions from one-dimensional mechanical point-by-point scanning to two-dimensional optical field measurement. By capturing the interference pattern across the entire mask surface simultaneously using optical detectors, the system achieves comprehensive characterization in a single measurement, eliminating the time-consuming sequential scanning process
2Measurement precision
If synchrotron EUV sources are used for mask characterization, then measurement precision is improved, but ease of manufacture deteriorates due to deployment difficulty
Solution Approach 1:
The patent replaces expensive, complex synchrotron EUV sources with more affordable, compact EUV light sources that can be integrated into standard manufacturing environments. The system uses commercially available EUV sources combined with optical gratings and detectors, eliminating the need for large-scale synchrotron facilities while achieving sufficient measurement precision for inline monitoring
Solution Approach 2:
The patent introduces an optical grating as an intermediary element between the EUV light source and the mask. The grating converts the EUV light into an interference pattern that encodes mask properties, enabling precise measurements without requiring direct access to high-brightness synchrotron radiation. This intermediary approach simplifies the overall system architecture and enables inline deployment
3Device complexity
If existing characterization methods are used, then device complexity is reduced, but loss of information increases due to insufficient mask performance data
Solution Approach 1:
The patent creates a multi-functional characterization system that simultaneously measures multiple mask properties through a single interference pattern analysis. The system can extract information about mask reflectivity, surface flatness, layer thickness, and other optical properties from the same measurement, providing comprehensive mask performance data without requiring multiple separate measurement systems
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 fast and cost-effective inline monitoring of mask quality during manufacturing, providing a reliable measure of mask performance through interference pattern analysis.
Implementation Method 1
arranged to illuminate a reflective or transmissive mask with light whereby mask-reflected or mask-transmitted light is generated
Implementation Method 2
an optical grating arranged to convert the mask-reflected or mask-transmitted light into an interference pattern
Implementation Method 3
an optical detector array arranged to generate an interference signal by measuring the interference pattern
Data Source
AI summary
A mask characterization method comprises measuring an interference signal of a reflection or transmission mask for use in lithography; and determining a quality metric for the reflection or transmission mask based on the interference signal. A mask characterization apparatus comprises a light source arranged to illuminate a reflective or transmissive mask with light whereby mask-reflected or mask-transmitted light is generated; an optical grating arranged to convert the mask-reflected or mask-transmitted light into an interference pattern; and an optical detector array arranged to generate an interference signal by measuring the interference pattern.