Small-Field Reflectivity Metrology for Fine Lithography Masks
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Solution Overview
Problem
Existing reflectometry methods struggle to accurately measure the reflectivity of very finely structured objects, such as lithography masks, with sufficient precision, particularly due to the need for precise determination of local reflectivity variations and the influence of pellicles.
Innovation Solution
A measurement method and metrology system that allows for a field of view smaller than 50 μm×50 μm, with a spatial resolution better than 100 nm, enabling precise measurement of local reflectivity variations and accounting for pellicle effects by using a Bertrand optical unit and energy sensors to normalize signal strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a larger field of view is used in reflectometry, then the measurement covers a larger area, but the precision for determining local reflectivity variations deteriorates
Solution Approach 1:
The patent divides the measurement process into multiple steps by scanning the object with the measurement light beam across different positions. Instead of capturing the entire object at once, the system segments the measurement into multiple localized measurements at different coordinates, each with a small field of view, thereby maintaining high precision for local reflectivity variations while still covering the entire object surface through systematic scanning.
Solution Approach 2:
The patent introduces a spatial scanning dimension to the measurement process. By moving the measurement light beam across the object surface in a controlled manner (scanning through different positions), the system transforms a single large-field measurement into multiple small-field measurements distributed across space, enabling precise local measurements while covering extended areas.
2Measurement precision
If the field of view is reduced to smaller than 50 μm×50 μm, then the precision for local reflectivity variations improves, but the measurement time and complexity increase
Solution Approach 1:
The patent implements continuous scanning of the measurement light beam across the object surface without interruption. The system maintains continuous measurement action by systematically moving the beam through different positions, eliminating idle time between measurements. This continuous scanning approach efficiently covers the entire object surface with small field of view measurements, reducing total measurement time while maintaining high local precision.
Solution Approach 2:
The patent employs dynamic scanning of the measurement light beam across the object surface. Instead of static large-field measurements, the system dynamically adjusts the beam position and scanning parameters to optimize measurement efficiency. The scanning mechanism adapts the measurement process to cover the entire object surface with small fields of view in a time-efficient manner.
3Area of stationary object
If the measurement light beam diameter is increased, then the coverage area improves, but the spatial resolution for detecting fine structures deteriorates
Solution Approach 1:
The patent segments the measurement process by using a small-diameter measurement light beam that scans across different positions on the object surface. Instead of using a single large-diameter beam to cover the entire area, the system divides the coverage into multiple small beam positions, each maintaining high spatial resolution for detecting fine structures while collectively covering the entire object surface through scanning.
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 precise measurement of local reflectivity variations in finely structured objects, allowing for accurate qualification of lithography masks and determination of pellicle influence, thereby improving the reliability of EUV lithography processes.
Implementation Method 1
a beam or bundle of measurement light (1) is impinged upon a section of an object (12) within a field of view (10) of the measurement apparatus (2)... The measurement light reflected by this section of the object (12) is captured
Data Source
AI summary
When measuring a reflectivity of an object for measurement light, initially the object and a reflectivity measurement apparatus are provided. The latter includes a measurement light source, an object holder for holding the object and a spatially resolving detector for capturing measurement light reflected by the object. A measurement light beam impinges on a section of the object within a field of view of the measurement apparatus. The reflected measurement light coming from the impinged-upon section of the object is captured. A surface area of the captured section is at most 50 μm×50 μm. The measurement is performed by the detector. Next, at least one reflectivity parameter of the object is determined on the basis of an intensity of the captured measurement light. The result is a measurement method and a metrology system operating therewith, whereby reflectivities in particular of very finely structured objects, such as lithography masks, can be measured with sufficient precision.